Observations of Rogue Seas in the Southern Ocean

We report direct observations of surface waves from a stereo camera system along with concurrent measurements of wind speed during an expedition across the Southern Ocean in the austral winter aboard the South African icebreaker S.A. Agulhas II. Records include water surface elevation across a range of wave conditions spanning from early stages of wave growth to full development. We give experimental evidence of rogue seas, i.e., sea states characterized by heavy tails of the probability density function well beyond the expectation based on bound mode theory. These conditions emerge during wave growth, where strong wind forcing and high nonlinearity drive wave dynamics. Quasiresonance wave-wave interactions, which are known to sustain the generation of large amplitude rogue waves, capture this behavior. Wave statistics return to normality as the wind forcing ceases and waves switch to a full developed condition.

Equilibrium and nonequilibrium description of negative temperature states in a one-dimensional lattice using a wave kinetic approach

We predict negative temperature states in the discrete nonlinear Schödinger (DNLS) equation as exact solutions of the associated wave kinetic equation. Within the wave kinetic approach, we define an entropy that results monotonic in time and reaches a stationary state, that is consistent with classical equilibrium statistical mechanics. We also perform a detailed analysis of the fluctuations of the actions at fixed wave numbers around their mean values. We give evidence that such fluctuations relax to their equilibrium behavior on a shorter timescale than the one needed for the spectrum to reach the equilibrium state. Numerical simulations of the DNLS equation are shown to be in agreement with our theoretical results. The key ingredient for observing negative temperatures in lattices characterized by two invariants is the boundedness of the dispersion relation.

Correction

This corrects the article DOI: 10.4088/JCP.09m05885blu.​​.

Spontaneous emergence of rogue waves in partially coherent waves: A quantitative experimental comparison between hydrodynamics and optics

Rogue waves are extreme and rare fluctuations of the wave field that have been discussed in many physical systems. Their presence substantially influences the statistical properties of a partially coherent wave field, i.e., a wave field characterized by a finite band spectrum with random Fourier phases. Their understanding is fundamental for the design of ships and offshore platforms. In many meteorological conditions waves in the ocean are characterized by the so-called Joint North Sea Wave Project (JONSWAP) spectrum. Here we compare two unique experimental results: the first one has been performed in a 270 m wave tank and the other in optical fibers. In both cases, waves characterized by a JONSWAP spectrum and random Fourier phases have been launched at the input of the experimental device. The quantitative comparison, based on an appropriate scaling of the two experiments, shows a very good agreement between the statistics in hydrodynamics and optics. Spontaneous emergence of heavy tails in the probability density function of the wave amplitude is observed in both systems. The results demonstrate the universal features of rogue waves and provide a fundamental and explicit bridge between two important fields of research. Numerical simulations are also compared with experimental results.

Wind Generated Rogue Waves in an Annular Wave Flume

We investigate experimentally the statistical properties of a wind-generated wave field and the spontaneous formation of rogue waves in an annular flume. Unlike many experiments on rogue waves where waves are mechanically generated, here the wave field is forced naturally by wind as it is in the ocean. What is unique about the present experiment is that the annular geometry of the tank makes waves propagating circularly in an unlimited-fetch condition. Within this peculiar framework, we discuss the temporal evolution of the statistical properties of the surface elevation. We show that rogue waves and heavy-tail statistics may develop naturally during the growth of the waves just before the wave height reaches a stationary condition. Our results shed new light on the formation of rogue waves in a natural environment.

Experimental Observation and Theoretical Description of Multisoliton Fission in Shallow Water

We observe the dispersive breaking of cosine-type long waves [Phys. Rev. Lett. 15, 240 (1965)] in shallow water, characterizing the highly nonlinear "multisoliton" fission over variable conditions. We provide new insight into the interpretation of the results by analyzing the data in terms of the periodic inverse scattering transform for the Korteweg-de Vries equation. In a wide range of dispersion and nonlinearity, the data compare favorably with our analytical estimate, based on a rigorous WKB approach, of the number of emerging solitons. We are also able to observe experimentally the universal Fermi-Pasta-Ulam recurrence in the regime of moderately weak dispersion.

Modulation Instability and Phase-Shifted Fermi-Pasta-Ulam Recurrence

Instabilities are common phenomena frequently observed in nature, sometimes leading to unexpected catastrophes and disasters in seemingly normal conditions. One prominent form of instability in a distributed system is its response to a harmonic modulation. Such instability has special names in various branches of physics and is generally known as modulation instability (MI). The MI leads to a growth-decay cycle of unstable waves and is therefore related to Fermi-Pasta-Ulam (FPU) recurrence since breather solutions of the nonlinear Schrödinger equation (NLSE) are known to accurately describe growth and decay of modulationally unstable waves in conservative systems. Here, we report theoretical, numerical and experimental evidence of the effect of dissipation on FPU cycles in a super wave tank, namely their shift in a determined order. In showing that ideal NLSE breather solutions can describe such dissipative nonlinear dynamics, our results may impact the interpretation of a wide range of new physics scenarios.

Gray solitons on the surface of water

The dynamics of surface gravity water waves can be described by the self-defocusing nonlinear Schrödinger equation. Recent observations of black solitons on the surface of water confirmed its validity for finite, below critical depth. The black soliton is a limiting case of a family of gray soliton solutions with finite amplitude depressions. Here, we report observations of gray solitons in water waves, thus, complementing our previous observations of black solitons.

Prevalence of pain-predominant functional gastrointestinal disorders and somatic symptoms in patients with anxiety or depressive disorders

OBJECTIVE

To determine whether children with symptoms of internalizing psychiatric disorders have a greater prevalence of pain-predominant functional gastrointestinal disorders (FGIDs) and migraine-like headaches.

STUDY DESIGN

Children and adolescents aged 6-18 years were recruited from a behavioral health center (n = 31) and a primary care center (n = 36). Subjects completed Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition-based symptom inventory questionnaires to screen for internalizing psychiatric disorders, the Questionnaire on Pediatric Gastrointestinal Symptoms, and a somatic distress assessment interview.

RESULTS

Thirty-three subjects (19 of 31 from the behavioral health center and 14 of 36 from the primary care center) screened positive for symptoms of anxiety or depressive disorders. The remainder screened negative and served as controls. Pain-predominant FGIDs were more common in the group with symptoms of anxiety or depression compared with controls (prevalence, 51.5% vs 8.8%; P = .0002). Migraine headaches occurred in 57.6% of the subjects with internalizing psychiatric disorders vs 23.5% of the control group (P = .006). The prevalence of functional constipation did not differ significantly between the 2 groups. The data remained essentially unchanged when analyzed within each center of recruitment.

CONCLUSION

Youths with anxiety or depressive symptoms are more likely to suffer from pain-predominant FGIDs and migraine-like headaches, but not from functional constipation. The lack of an association between functional constipation and internalizing psychiatric symptoms suggests that FGIDs associated with pain may bear a specific relationship to emotional disorders.

Hydrodynamic supercontinuum

We report the experimental observation of multi-bound-soliton solutions of the nonlinear Schrödinger equation (NLS) in the context of hydrodynamic surface gravity waves. Higher-order N-soliton solutions with N=2, 3 are studied in detail and shown to be associated with self-focusing in the wave group dynamics and the generation of a steep localized carrier wave underneath the group envelope. We also show that for larger input soliton numbers, the wave group experiences irreversible spectral broadening, which we refer to as a hydrodynamic supercontinuum by analogy with optics. This process is shown to be associated with the fission of the initial multisoliton into individual fundamental solitons due to higher-order nonlinear perturbations to the NLS. Numerical simulations using an extended NLS model described by the modified nonlinear Schrödinger equation, show excellent agreement with experiment and highlight the universal role that higher-order nonlinear perturbations to the NLS play in supercontinuum generation.

Super-rogue waves in simulations based on weakly nonlinear and fully nonlinear hydrodynamic equations

The rogue wave solutions (rational multibreathers) of the nonlinear Schrödinger equation (NLS) are tested in numerical simulations of weakly nonlinear and fully nonlinear hydrodynamic equations. Only the lowest order solutions from 1 to 5 are considered. A higher accuracy of wave propagation in space is reached using the modified NLS equation, also known as the Dysthe equation. This numerical modeling allowed us to directly compare simulations with recent results of laboratory measurements in Chabchoub et al. [Phys. Rev. E 86, 056601 (2012)]. In order to achieve even higher physical accuracy, we employed fully nonlinear simulations of potential Euler equations. These simulations provided us with basic characteristics of long time evolution of rational solutions of the NLS equation in the case of near-breaking conditions. The analytic NLS solutions are found to describe the actual wave dynamics of steep waves reasonably well.

Modulational instability, wave breaking, and formation of large-scale dipoles in the atmosphere

We use direct numerical simulation of the Navier-Stokes equations for a two-phase flow (water and air) to study the dynamics of the modulational instability of free surface waves and its contribution to the interaction between the ocean and atmosphere. If the steepness of the initial wave exceeds a threshold value, we observe wave-breaking events and the formation of large-scale dipole structures in the air. Because of the multiple steepening and breaking of the waves under unstable wave packets, a train of dipoles is released in the atmosphere; those dipoles propagate at a height comparable with the wavelength. The amount of energy dissipated by the breaker in water and air is considered, and contrary to expectations, we observe that the energy dissipation in air is greater than that in water. The possible consequences on the wave modeling and on the exchange of aerosols and gases between air and water are discussed.

Excitation of rogue waves in a variable medium: an experimental study on the interaction of water waves and currents

We show experimentally that a stable wave propagating into a region characterized by an opposite current may become modulationally unstable. Experiments have been performed in two independent wave tank facilities; both of them are equipped with a wavemaker and a pump for generating a current propagating in the opposite direction with respect to the waves. The experimental results support a recent conjecture based on a current-modified nonlinear Schrödinger equation which establishes that rogue waves can be triggered by a nonhomogeneous current characterized by a negative horizontal velocity gradient.

Experimental observation of dark solitons on the surface of water

We present the first ever observation of dark solitons on the surface of water. It takes the form of an amplitude drop of the carrier wave which does not change shape in propagation. The shape and width of the soliton depend on the water depth, carrier frequency, and the amplitude of the background wave. The experimental data taken in a water tank show an excellent agreement with the theory. These results may improve our understanding of the nonlinear dynamics of water waves at finite depths.

Observation of a hierarchy of up to fifth-order rogue waves in a water tank

We present experimental observations of the hierarchy of rational breather solutions of the nonlinear Schrödinger equation (NLS) generated in a water wave tank. First, five breathers of the infinite hierarchy have been successfully generated, thus confirming the theoretical predictions of their existence. Breathers of orders higher than five appeared to be unstable relative to the wave-breaking effect of water waves. Due to the strong influence of the wave breaking and relatively small carrier steepness values of the experiment these results for the higher-order solutions do not directly explain the formation of giant oceanic rogue waves. However, our results are important in understanding the dynamics of rogue water waves and may initiate similar experiments in other nonlinear dispersive media such as fiber optics and plasma physics, where the wave propagation is governed by the NLS.

Out of the black box: treatment of resistant depression in adolescents and the antidepressant controversy

OBJECTIVE

The purpose of this article is to describe the effects of the pediatric antidepressant controversy on the Treatment of Serotonin-Selective Reuptake Inhibitor (SSRI) Resistant Depression in Adolescents (TORDIA) trial.

METHOD

Adolescents, ages 12-18 years, with SSRI resistant depression were randomized to one of four treatments for a 12 week trial: Switch to different SSRI, switch to an alternate antidepressant (venlafaxine), switch to an alternate SSRI plus cognitive behavior therapy (CBT), or switch to venlafaxine plus CBT.

RESULTS

The health advisories and "black box" warnings regarding suicidality and antidepressants in adolescents occurred during the course of the TORDIA trial. Revisions to the protocol, multiple-consent form changes, and re-consenting of patients were necessary. Recruitment of participants was adversely affected.

CONCLUSION

Despite a cascade of unforeseen events that delayed the completion of the study, the TORDIA trial resulted in clinically important information about treatment-resistant depression in adolescents.

Incremental cost-effectiveness of combined therapy vs medication only for youth with selective serotonin reuptake inhibitor-resistant depression: treatment of SSRI-resistant depression in adolescents trial findings

CONTEXT

Many youth with depression do not respond to initial treatment with selective serotonin reuptake inhibitors (SSRIs), and this is associated with higher costs. More effective treatment for these youth may be cost-effective.

OBJECTIVE

To evaluate the incremental cost-effectiveness over 24 weeks of combined cognitive behavior therapy plus switch to a different antidepressant medication vs medication switch only in adolescents who continued to have depression despite adequate initial treatment with an SSRI.

DESIGN

Randomized controlled trial.

SETTING

Six US academic and community clinics.

PATIENTS

Three hundred thirty-four patients aged 12 to 18 years with SSRI-resistant depression.

INTERVENTION

Participants were randomly assigned to (1) switch to a different medication only or (2) switch to a different medication plus cognitive behavior therapy.

MAIN OUTCOME MEASURES

Clinical outcomes were depression-free days (DFDs), depression-improvement days (DIDs), and quality-adjusted life-years based on DFDs (DFD-QALYs). Costs of intervention, nonprotocol services, and families were included.

RESULTS

Combined treatment achieved 8.3 additional DFDs (P = .03), 0.020 more DFD-QALYs (P = .03), and 11.0 more DIDs (P = .04). Combined therapy cost $1633 more (P = .01). Cost per DFD was $188 (incremental cost-effectiveness ratio [ICER] = $188; 95% confidence interval [CI], -$22 to $1613), $142 per DID (ICER = $142; 95% CI, -$14 to $2529), and $78,948 per DFD-QALY (ICER = $78,948; 95% CI, -$9261 to $677,448). Cost-effectiveness acceptability curve analyses suggest a 61% probability that combined treatment is more cost-effective at a willingness to pay $100,000 per QALY. Combined treatment had a higher net benefit for subgroups of youth without a history of abuse, with lower levels of hopelessness, and with comorbid conditions.

CONCLUSIONS

For youth with SSRI-resistant depression, combined treatment decreases the number of days with depression and is more costly. Depending on a decision maker's willingness to pay, combined therapy may be cost-effective, particularly for some subgroups.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00018902.

Long-term outcome of adolescent depression initially resistant to selective serotonin reuptake inhibitor treatment: a follow-up study of the TORDIA sample

BACKGROUND

We examined the long-term outcome of participants in the Treatment of SSRI-Resistant Depression in Adolescents (TORDIA) study, a randomized trial of 334 adolescents (aged 12-18 years) with DSM-IV-defined major depressive disorder initially resistant to selective serotonin reuptake inhibitor (SSRI) treatment who were subsequently treated for 12 weeks with another SSRI, venlafaxine, another SSRI + cognitive-behavioral therapy (CBT), or venlafaxine + CBT. Responders then continued with the same treatment through week 24, while nonresponders were given open treatment.

METHOD

For the current study, patients were reassessed 48 (n = 116) and 72 (n = 130) weeks from intake. Data were gathered from February 2001 to February 2007. Standardized diagnostic interviews and measures of depression, suicidal ideation, related psychopathology, and level of functioning were periodically administered. Remission was defined as ≥ 3 weeks with ≤ 1 clinically significant symptom and no associated functional impairment (score of 1 on the adolescent version of the Longitudinal Interval Follow-Up Evaluation [A-LIFE]), and relapse, as ≥ 2 weeks with probable or definite depressive disorder (score of 3 or 4 on the A-LIFE). Mixed-effects regression models were applied to estimate remission, relapse, and functional recovery.

RESULTS

By 72 weeks, an estimated 61.1% of the randomized youths had reached remission. Randomly assigned treatment (first 12 weeks) did not influence remission rate or time to remission, but the group assigned to SSRIs had a more rapid decline in self-reported depressive symptoms and suicidal ideation than those assigned to venlafaxine (P < .03). Participants with more severe depression, greater dysfunction, and alcohol or drug use at baseline were less likely to remit. The depressive symptom trajectory of the remitters diverged from that of nonremitters by the first 6 weeks of treatment (P < .001). Of the 130 participants in remission at week 24, 25.4% relapsed in the subsequent year.

CONCLUSIONS

While most adolescents achieved remission, more than one-third did not, and one-fourth of remitted patients experienced a relapse. More effective interventions are needed for patients who do not show robust improvement early in treatment.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00018902.

Treatment of Resistant Depression in Adolescents (TORDIA): week 24 outcomes

OBJECTIVE

The purpose of this study was to report on the outcome of participants in the Treatment of Resistant Depression in Adolescents (TORDIA) trial after 24 weeks of treatment, including remission and relapse rates and predictors of treatment outcome.

METHOD

Adolescents (ages 12-18 years) with selective serotonin reuptake inhibitor (SSRI)-resistant depression were randomly assigned to either a medication switch alone (alternate SSRI or venlafaxine) or a medication switch plus cognitive-behavioral therapy (CBT). At week 12, responders could continue in their assigned treatment arm and nonresponders received open treatment (medication and/or CBT) for 12 more weeks (24 weeks total). The primary outcomes were remission and relapse, defined by the Adolescent Longitudinal Interval Follow-Up Evaluation as rated by an independent evaluator.

RESULTS

Of 334 adolescents enrolled in the study, 38.9% achieved remission by 24 weeks, and initial treatment assignment did not affect rates of remission. Likelihood of remission was much higher (61.6% versus 18.3%) and time to remission was much faster among those who had already demonstrated clinical response by week 12. Remission was also higher among those with lower baseline depression, hopelessness, and self-reported anxiety. At week 12, lower depression, hopelessness, anxiety, suicidal ideation, family conflict, and absence of comorbid dysthymia, anxiety, and drug/alcohol use and impairment also predicted remission. Of those who responded by week 12, 19.6% had a relapse of depression by week 24.

CONCLUSIONS

Continued treatment for depression among treatment-resistant adolescents results in remission in approximately one-third of patients, similar to adults. Eventual remission is evident within the first 6 weeks in many, suggesting that earlier intervention among nonresponders could be important.

Association of FKBP5 polymorphisms with suicidal events in the Treatment of Resistant Depression in Adolescents (TORDIA) study

OBJECTIVE

The authors sought to assess the relationship between candidate genes and two clinical outcomes, namely, symptomatic improvement and the occurrence of suicidal events, in a sample of treatment-resistant depressed adolescents.

METHOD

A subsample of depressed adolescents participating in the Treatment of SSRI-Resistant Depression in Adolescents (TORDIA) trial, 155 of whom were of European origin, were genotyped with respect to 21 polymorphisms on 12 genes that have a reported association with depression, treatment response, or suicidal events. Participants had not responded to a previous adequate trial with an antidepressant and were randomized to receive either another selective serotonin reuptake inhibitor or venlafaxine, with or without cognitive-behavioral therapy (CBT). Single-nucleotide polymorphism (SNP) analyses were conducted using PLINK with permutation procedures.

RESULTS

No relationship was observed between any polymorphism and response to treatment. The FKBP5 (which codes for a protein causing subsensitivity of the glucocorticoid receptor) rs1360780TT and rs3800373GG genotypes were associated with suicidal events (N=18), even after controlling for treatment effects and relevant covariates. These two SNPs were in significant linkage disequilibrium (r=0.91).

CONCLUSIONS

The FKBP5 genotypes associated with suicidal events in this study have been reported by others to cause the greatest degree of glucocorticoid receptor subsensitivity. These results are consistent with those of other studies linking alterations in the hypothalamic-pituitary-adrenal axis with suicidal behavior. The small number of events and lack of a placebo condition make these results preliminary. Replication with a larger sample and a placebo condition is needed to assess whether these events are related to treatment.

Predictors of spontaneous and systematically assessed suicidal adverse events in the treatment of SSRI-resistant depression in adolescents (TORDIA) study

OBJECTIVE

The authors sought to identify predictors of self-harm adverse events in treatment-resistant, depressed adolescents during the first 12 weeks of treatment.

METHOD

Depressed adolescents (N=334) who had not responded to a previous trial with an SSRI antidepressant were randomized to a switch to either another SSRI or venlafaxine, with or without cognitive behavior therapy. Self-harm events, i.e., suicidal and non-suicidal self-injury adverse events were assessed by spontaneous report for the first 181 participants, and by systematic weekly assessment for the last 153 participants.

RESULTS

Higher rates of suicidal (20.8% vs. 8.8%) and nonsuicidal self-injury (17.6% vs. 2.2%), but not serious adverse events (8.4% vs. 7.3%) were detected with systematic monitoring. Median time to a suicidal event was 3 weeks, predicted by high baseline suicidal ideation, family conflict, and drug and alcohol use. Median time to nonsuicidal self-injury was 2 weeks, predicted by previous history of nonsuicidal self-injury. While there were no main effects of treatment, venlafaxine treatment was associated with a higher rate of self-harm adverse events in those with higher suicidal ideation. Adjunctive use of benzodiazepines, while in a small number of participants (N=10) was associated with higher rate of both suicidal and nonsuicidal self-injury adverse events.

CONCLUSIONS

Since predictors of suicidal adverse events also predict poor response to treatment, and many of these events occurred early in treatment, improving the speed of response to depression, by targeting of family conflict, suicidal ideation, and drug use may help to reduce their incidence. The relationship of venlafaxine and of benzodiazepines to self-harm events requires further study and clinical caution.

Statistical properties of directional ocean waves: the role of the modulational instability in the formation of extreme events

We discuss two independent, large scale experiments performed in two wave basins of different dimensions in which the statistics of the surface wave elevation are addressed. Both facilities are equipped with a wave maker capable of generating waves with prescribed frequency and directional properties. The experimental results show that the probability of the formation of large amplitude waves strongly depends on the directional properties of the waves. Sea states characterized by long-crested and steep waves are more likely to be populated by freak waves with respect to those characterized by a large directional spreading.

Switching to another SSRI or to venlafaxine with or without cognitive behavioral therapy for adolescents with SSRI-resistant depression: the TORDIA randomized controlled trial

CONTEXT

Only about 60% of adolescents with depression will show an adequate clinical response to an initial treatment trial with a selective serotonin reuptake inhibitor (SSRI). There are no data to guide clinicians on subsequent treatment strategy.

OBJECTIVE

To evaluate the relative efficacy of 4 treatment strategies in adolescents who continued to have depression despite adequate initial treatment with an SSRI.

DESIGN, SETTING, AND PARTICIPANTS

Randomized controlled trial of a clinical sample of 334 patients aged 12 to 18 years with a primary diagnosis of major depressive disorder that had not responded to a 2-month initial treatment with an SSRI, conducted at 6 US academic and community clinics from 2000-2006.

INTERVENTIONS

Twelve weeks of: (1) switch to a second, different SSRI (paroxetine, citalopram, or fluoxetine, 20-40 mg); (2) switch to a different SSRI plus cognitive behavioral therapy; (3) switch to venlafaxine (150-225 mg); or (4) switch to venlafaxine plus cognitive behavioral therapy.

MAIN OUTCOME MEASURES

Clinical Global Impressions-Improvement score of 2 or less (much or very much improved) and a decrease of at least 50% in the Children's Depression Rating Scale-Revised (CDRS-R); and change in CDRS-R over time.

RESULTS

Cognitive behavioral therapy plus a switch to either medication regimen showed a higher response rate (54.8%; 95% confidence interval [CI], 47%-62%) than a medication switch alone (40.5%; 95% CI, 33%-48%; P = .009), but there was no difference in response rate between venlafaxine and a second SSRI (48.2%; 95% CI, 41%-56% vs 47.0%; 95% CI, 40%-55%; P = .83). There were no differential treatment effects on change in the CDRS-R, self-rated depressive symptoms, suicidal ideation, or on the rate of harm-related or any other adverse events. There was a greater increase in diastolic blood pressure and pulse and more frequent occurrence of skin problems during venlafaxine than SSRI treatment.

CONCLUSIONS

For adolescents with depression not responding to an adequate initial treatment with an SSRI, the combination of cognitive behavioral therapy and a switch to another antidepressant resulted in a higher rate of clinical response than did a medication switch alone. However, a switch to another SSRI was just as efficacious as a switch to venlafaxine and resulted in fewer adverse effects.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00018902.

Why there is a need of an ethics committee in scientific medical societies

Scientific associations involved in clinical activities are responsible to their members and to the medical community when using new drugs or technologies in clinical practice. Any new procedure or clinical use of new drugs represents a form of research and should adhere to guidelines defined by an ethics committee. It is therefore important that all medical scientific societies should establish an ethics committee. The ethics committee should be in direct contact with the scientific or research committee of the society to evaluate if a clinical trial is useful and not dangerous for patients. A group of expert members of this committee should advise the best method to avoid harm or discomfort to the patient. This gives the best guarantee and can evaluate the real progress of such a new procedure for the benefit of the patient.

Modulational instability in crossing sea states: a possible mechanism for the formation of freak waves

Here we consider a simple weakly nonlinear model that describes the interaction of two-wave systems in deep water with two different directions of propagation. Under the hypothesis that both sea systems are narrow banded, we derive from the Zakharov equation two coupled nonlinear Schrödinger equations. Given a single unstable plane wave, here we show that the introduction of a second plane wave, propagating in a different direction, can result in an increase of the instability growth rates and enlargement of the instability region. We discuss these results in the context of the formation of rogue waves.

Observation of strongly non-Gaussian statistics for random sea surface gravity waves in wave flume experiments

We study random surface gravity wave fields and address the formation of large-amplitude waves in a laboratory environment. Experiments are performed in one of the largest wave tank facilities in the world. We present experimental evidence that the tail of the probability density function for wave height strongly depends on the Benjamin-Feir index (BFI)-i.e., the ratio between wave steepness and spectral bandwidth. While for a small BFI the probability density functions obtained experimentally are consistent with the Rayleigh distribution, for a large BFI the Rayleigh distribution clearly underestimates the probability of large events. These results confirm experimentally the fact that large-amplitude waves in random spectra may result from the modulational instability.

Peracetic acid as an alternative wastewater disinfectant to chlorine dioxide

AIMS

The aim of this study was to compare the efficiency of peracetic acid with that of chlorine dioxide in the disinfection of wastewater from a sewage treatment plant (serving about 650 000 inhabitants) that has been using peracetic acid as a disinfectant since 1998.

METHODS AND RESULTS

A total of 23 samplings were made, each consisting of three samples: from secondary effluent, effluent disinfected with 2 mg l(-1) of peracetic acid and effluent disinfected with 2.2 mg l(-1) of chlorine dioxide (contact time 20 min). For each sample, measurements were made of the heterotrophic plate count at 36 degrees C, total and faecal coliforms, Escherichia coli, enterococci, pH, suspended solids and chemical oxygen demand (COD). During the first phase of the experiment the peracetic acid was seen to be less efficient than chlorine dioxide. To improve the disinfectant action a system of mechanical agitation was added which led to a greater efficiency in the inactivation of bacteria of faecal origin.

CONCLUSIONS

Both products were found to be influenced by the level of microbial contamination, the amount of suspended solids and COD but not by the pH of the effluent before disinfection. The immediate mixing of the wastewater and disinfectant caused a greater reduction in enterococci.

SIGNIFICANCE AND IMPACT OF THE STUDY

Since peracetic acid was seen to produce a high abatement of micro-organisms, it can be considered as a valid alternative to chlorine dioxide in the disinfection of wastewaters.

Freely decaying weak turbulence for sea surface gravity waves

We study the long-time evolution of deep-water ocean surface waves in order to better understand the behavior of the nonlinear interaction processes that need to be accurately predicted in numerical models of wind-generated ocean surface waves. Of particular interest are those nonlinear interactions which are predicted by weak turbulence theory to result in a wave energy spectrum of the form of [k](-2.5). We numerically implement the primitive Euler equations for surface waves and demonstrate agreement between weak turbulence theory and the numerical results.

Freak waves in random oceanic sea states

Freak waves are very large, rare events in a random ocean wave train. Here we study their generation in a random sea state characterized by the Joint North Sea Wave Project spectrum. We assume, to cubic order in nonlinearity, that the wave dynamics are governed by the nonlinear Schrödinger (NLS) equation. We show from extensive numerical simulations of the NLS equation how freak waves in a random sea state are more likely to occur for large values of the Phillips parameter alpha and the enhancement coefficient gamma. Comparison with linear simulations is also reported.

Testicular atrophy in 80 HIV-positive patients: a multivariate statistical analysis

This retrospective study of risk factors for testicular atrophy in HIV-infected men investigates the relationship between complications of AIDS such as wasting or opportunistic illness and testicular atrophy. Microscopic sections of the right testis were evaluated for testicular atrophy by assessing the mean score in each of 80 selected HIV-infected patients who underwent an autopsy during a one-year period. A significant association was observed between testicular atrophy and body mass index (BMI) (P=0.0496). Thus, underweight patients with HIV infection were 3.52 times more likely to have testicular atrophy than those with acceptable body weight. Other significant associations between other variables were not found.

Probability density function and "plus" and "minus" structure functions in a turbulent channel flow

We consider the statistical properties of the longitudinal velocity increments in a turbulent channel flow at different distances from the wall. The probability density function (PDF) of the velocity difference of the streamwise component near the wall are found to be, especially at small scales, strongly skewed, showing a very long left tail. We consider "plus" and "minus" structure functions and compute separately the statistics for the right and left part of the PDF. It is found that the relative scaling exponents for the right tail are less affected by the presence of the wall and their values are consistent with the ones found in experiments in homogeneous and isotropic turbulence. A simple phenomenological model that explains the results obtained is also given.

Gallstones in elderly patients: impact of laparoscopic cholecystectomy

The use of laparoscopic cholecystectomy (LC) in elderly patients may pose problems because of their poor general condition, especially of cardiopulmonary function. Moreover, these patients present with acute cholecystitis and associated common bile duct stones more often than their younger counterparts. From 1990 to 1999, the authors performed 943 LCs; 31 (3.2%) were attempted on elderly patients, 11 (35%) of which were on an emergency basis because of acute cholecystitis, cholangitis or acute biliary pancreatitis. Ten per cent of LCs needed to be converted to an open cholecystectomy, most often because of an increase in the partial pressure of carbon dioxide in the blood produced by excessive operative time. A gasless procedure was used in the last three years of the study on eight cases; the overall rate of conversion from LC to open cholecystectomy in this group was 0%. Associated gallbladder and common bile duct stones were found in five (16%) patients (four preoperative LC endoscopic sphincterotomy and one transcystic approach). The success rate in both of these cases was 100%, overall morbidity was 29% and there was no mortality. These results show that LC is a feasible and safe procedure for use in elderly patients. Gasless LC should be preferred in patients classified as American Society of Anesthesiologists' class III because an excessive duration of operation is the most common reason for converting to an open cholecystectomy.

Small scale intermittency and bursting in a turbulent channel flow

The statistical properties of the streamwise velocity fluctuations in a fully developed turbulent channel flow are studied experimentally by means of single hot wire measurements. The intermittency features, studied through the scaling of the moments of the velocity structure function computed using the extended self- similarity and through the probability density function of the wavelet coefficients, are found to be dependent on the distance from the wall. The maximum intermittency effects are observed in the region between the buffer layer and the inner part of the logarithmic region where it is known that the bursting phenomenon, related to coherent structures such as low speed streaks and streamwise vortices, is the dominant dynamical feature. An eduction technique based on wavelet transform for identification of organized motion is developed and used to analyze the turbulent signals. Streamwise velocity conditional averages computed on events educed with the proposed method are reported. Events responsible for intermittency are found to consist of regions of high velocity gradients and are directly correlated with the observed increase of intermittency close to the wall.

Endoscopic and surgical integration in the approach to biliary tract disease

Several techniques are available today to access the bile ducts, all equally safe and effective. Since 1990, we have studied three groups of patients treated with different methods: the sequential endoscopic sphincterotomy + laparoscopic cholecystectomy, the single-stage laparoscopic approach, and the single laparoscopic-endoscopic approach. The results obtained in 127 patients to date suggest that one single-stage treatment is more convenient for the patient, while the combination of endoscopic sphincterotomy with laparoscopic cholecystectomy is preferable in terms of efficacy and safety.

Risk factors for colonization or infection due to methicillin-resistant Staphylococcus aureus in HIV-positive patients: a retrospective case-control study

OBJECTIVE

To determine the risk factors for colonization or infection with methicillin-resistant Staphylococcus aureus in human immunodeficiency virus (HIV)-infected patients.

DESIGN

Retrospective matched-pair case-control study.

SETTING

Continuity clinic and inpatient HIV service of a university medical center.

POPULATION

Patients with HIV infection from the general population of eastern and coastal Texas and from the Texas Department of Criminal Justice.

DATA COLLECTION

Patient charts and the AIDS Care and Clinical Research Program Database were reviewed for the following: age, race, number of admissions, total hospital days, presence of a central venous catheter, serum albumin, total white blood cell count and absolute neutrophil count, invasive or surgical procedures, any cultures positive for S. aureus, and a history of opportunistic illnesses, diabetes, or dermatologic diagnoses. Data also were collected on the administration of antibiotics, antiretroviral therapy, steroids, cancer chemotherapy, and subcutaneous medications.

RESULTS

In the univariate analysis, the presence of a central venous catheter, an underlying dermatologic disease, lower serum albumin, prior steroid therapy, and prior antibiotic therapy, particularly antistaphylococcal therapy or multiple courses of antibiotics, were associated with increased risk for colonization or infection with methicillin-resistant S. aureus. Multivariate analysis yielded a model that included presence of a central venous catheter, underlying dermatologic disease, broad-spectrum antibiotic exposure, and number of hospital days as independent risk factors for colonization or infection with methicillin-resistant S. aureus.

CONCLUSIONS

In our HIV-infected patient population, prior hospitalization, exposure to broad-spectrum antibiotics, presence of a central venous catheter, and dermatologic disease were risk factors for acquisition of methicillin-resistant S. aureus.

[Endolaparoscopic "Rendez-vous" in the treatment of cholecysto-choledochal calculosis]

Different methods, all of which equally efficacious and safe, can be selected to access the choledochus in patients with cholecysto and choledocholithiasis on the basis of clinical and anatomosurgical parameters. From 1990 we evaluated three groups of patients who underwent surgery at different times and with different methods: sequentially (endoscopic sphincterotomy and laparoscopic cholecystectomy), one step laparoscopy and combined laparo-endoscopy. The results obtained seem to show that the treatment with laparoscopy alone is the most advantageous in terms of cost-benefit, while the endoscopic access of the choledochus during laparoscopic cholecystectomy is the one to prefer in terms of efficacy and safety.

[A case of anaplastic carcinoma of the thyroid. Clinico-pathological and therapeutic aspects and review of the literature]

A case of anaplastic carcinoma of the thyroid observed in a 72-year-old female patient, admitted with previous diagnosis of Riedel's thyroiditis, is reported. Clinicopathologic features and management of this rare neoplasm are discussed and Literature is reviewed. Anaplastic cancer is a locally and systemically aggressive histologic type, occurring more frequently in older patients and in those with a history of benign and/or malignant thyroid disease. Because long-term survival was seen most commonly in well-localized anaplastic tumors, a more aggressive approach to thyroid lesions, especially in the elderly, may be warranted to improve early diagnosis and effectiveness of therapy of this nearly always lethal neoplasm. Although patients can rarely be cured, efforts should be made to control the disease locally by combined treatment including surgery and radiochemotherapy, which is found to be, at times, a national palliative therapeutic approach despite patient's advanced age.

An approach to antiretroviral treatment of HIV disease. New approaches

Viral resistance limits the value of drugs that act through competitive inhibition of HIV reverse transcriptase (RT). Thus, the emphasis of current research is on agents with other mechanisms. The possibilities include noncompetitive RT inhibitors, drugs against an entirely different enzyme--HIV proteinase, and measures to enhance immunity, either globally or against HIV specifically.

In vitro production of leukemia inhibitory factor (LIF) by Hep G2 hepatoblastoma cells

This study shows that the human hepatoblastoma cell line Hep G2 constitutively expressed a high level of Leukemia Inhibitory Factor (LIF) mRNA in the characteristic major 3.8 and minor 1.8 Kb forms. DNA analysis of the LIF gene from Hep G2 revealed no rearrangements. Production and secretion of significant concentrations of LIF were demonstrated by enzyme-linked immunoabsorbent assay (ELISA) in culture supernatants of Hep G2 cells. The highest LIF concentration in culture was found at 48-h (250 pg/ml). LIF produced by Hep G2 cells was biologically active since cell-free culture supernatants were able to induce in vitro differentiation of the M1 murine myeloid leukemia cell line. On the contrary, no LIF mRNA expression was detected in normal liver cells by PCR analysis. Our results suggest that LIF acts on normal parenchymal hepatocytes through a paracrine mechanism and on Hep G2 cells by an autocrine action. Furthermore they indicate that the Hep G2 cell line could be an useful model for studying the LIF autocrine mechanism in hepatomas.

Neuropil threads of Alzheimer's disease show a marked alteration of the normal cytoskeleton

Abnormal neurites, neuropil threads, are a widespread and characteristic lesion of Alzheimer's disease likely to play a major role in the cognitive impairment of this disease. Contrary to normal neurites, neuropil threads contain straight and paired helical filaments that contain the microtubule-associated protein tau and ubiquitin. It is not known whether these abnormal filaments are added to or replace the normal cytoskeleton. In this study, we examined the fine structure of neuropil threads and carried out a morphometric analysis of the neurofilaments and abnormal filaments contained in the neuropil threads by using an antiserum to tau and colloidal gold immuno-electron microscopy. Almost 70% of the neuropil threads contained straight or paired helical filaments with no neurofilaments. The total number of filaments in each neuropil thread remained essentially unchanged either when straight or paired helical filaments were present alone or when they coexisted either together or with neurofilaments. When the three types of filaments were expressed as a proportion of the total, a linear inverse correlation was found between neurofilaments and straight filaments as well as between straight and paired helical filaments. Approximately 10% of the neuropil threads were found to be myelinated axons. It is concluded that straight filaments are likely to replace neurofilaments, that they in turn might be replaced by paired helical filaments, and that this process occurs in axons as well as dendrites.

Activation of the granulocyte-monocyte colony stimulating factor gene in acute myeloid leukaemia cells is not related to gene rearrangement

Several reports have documented that leukaemic blasts produce a number of cytokines among them the granulocyte-monocyte colony stimulating factor (GM-CSF). We analysed the structure of the gene that codes for GM-CSF in 44 acute myeloid leukaemia (AML) cases in an attempt to establish whether the autocrine production of GM-CSF was due to a structural gene alteration. No structural alteration was detected in the GM-CSF gene in any of the 44 cases studied. We, therefore, conclude that the autocrine production of GM-CSF by leukaemia blasts is not dependent on gene rearrangement.

The widespread alteration of neurites in Alzheimer's disease may be unrelated to amyloid deposition

The structural changes of Alzheimer's disease (AD) include a widespread alteration of neuronal cell processes in addition to senile plaques and neurofibrillary tangles. Since the antigenic characteristics of these abnormal neurites are similar to those of the abnormal neurites associated with the senile plaques, the question has been raised as to whether the widespread neuritic alteration is secondary to the deposition of amyloid. To answer this question, we examined brains from 2 subjects with a longer-lasting form of subacute sclerosing panencephalitis (SSPE) characterized by the presence of numerous neurofibrillary tangles but no senile plaques, 3 subjects with AD, and 2 age-matched controls. Light and electron immunocytochemical analyses revealed that abnormal neurites are present diffusely in SSPE cerebral cortex in the absence of amyloid deposits. These abnormal neurites were qualitatively identical to the widespread abnormal neurites of AD. The abnormal neurites, in contrast to the neurites of control brains, immunoreacted with antibodies to tau and ubiquitin. These distinctive antigenic features were due to the presence in these abnormal neurites of straight filaments, 14 to 16 nm in diameter, mixed with a few paired helical filaments. The spatial distribution of the widespread neuritic alteration correlated with that of neurofibrillary tangles in both conditions, but not with that of senile plaques in AD. The present findings demonstrate that a diffuse alteration of neurites similar to that present in AD takes place independently of the deposition of amyloid in SSPE, and they are consistent with the hypothesis that in AD, also, this alteration is not secondary to the deposition of amyloid.(ABSTRACT TRUNCATED AT 250 WORDS)