Computational Study of the Structure and Transport in Pyrrolidinium-Li-TFSI-Silica Ionogels

Ionogels (IGs) are a unique class of composite materials with attributes that make them promising materials for applications in electrochemical energy storage. Due to the solid porous matrix that confines the ionic liquid (IL) in the IG, they can be used as self-supporting electrolytes. Furthermore, interactions of the IL with the porous matrix can have beneficial effects on transport, such as lowering the freezing/glass transition temperature of the conducting IL. In this work, we employ molecular dynamics simulations to investigate the influence of the porous morphology and solid volume fraction on ionic conductivity and Li⁺ diffusivity using a representative 0.5 M Li-bis(trifluoromethane)sulfonimide (TFSI)-pyrrolidinium (Pyr1.3) IL confined in a nanoporous silica matrix. The effect of the morphology of the confining matrix is compared using the pure IL as a baseline. We find that the tracer and collective Li⁺ diffusion and ionic conductivity of all the model IGs have significantly lower temperature dependence than the corresponding pure IL. In general, low-silica IGs with wide pores displayed the best transport properties at high temperatures, but the trends with the morphology for the nested set of transport coefficients we examined changed as the collective behavior of the Li⁺ ions and the molecular IL components were considered. Remarkably, some of the model IGs displayed better transport properties on a volume of fluid basis at low temperatures than the constituent IL. These trends were tied to structural changes revealed by the radial distribution functions of the IL components and the silica surface, including a decreasing Li⁺ adsorption peak of the surface silica indicating a change in the relative contributions of bulk-like and surface-like transport in the confined IL.

Effects of Strain Rate and Temperature on the Mechanical Properties of Simulated Silica Ionogels

Ionogels are hybrid materials formed by impregnating the pore space of a solid matrix with a conducting ionic liquid. By combining the properties of both component materials, ionogels can act as self-supporting electrolytes in Li batteries. In this study, molecular dynamics simulations are used to investigate the dependence of mechanical properties of silica ionogels on solid fraction, temperature, and pore width. Comparisons are made with corresponding aerogels. We find that the solid matrix fraction increases the moduli and strength of the ionogel. This varies nonlinearly with temperature and strain rate, according to the contribution of the viscous ionic liquid to resisting deformation. Owing to the temperature and strain sensitivity of the ionic liquid viscosity, the mechanical properties approach a linear mixing law at high temperature and low strain rates. The median pore width of the solid matrix plays a complex role, with its influence varying qualitatively with deformation mode. Narrower pores increase the relevant elastic modulus under shear and uniaxial compression but reduce the modulus obtained under uniaxial tension. Conversely, shear and tensile strength are increased by narrowing the pore width. All of these pore size effects become more pronounced as the silica fraction increases. Pore size effects, similar to the effects of temperature and strain rate, are linked to the ease of fluid redistribution within the pore space during deformation-induced changes in the geometry of the pores.

Tensegrity Structures Prestressability Investigation

A methodology for the investigation of tensegrity structures prestressability is presented. The methodology is aimed at identifying particular prestressable configurations for which the prestressability conditions can be expressed in a simple form. Examples of the application of the methodology to a class of tensegrity structures, called tensegrity towers, are presented.

3-D nanomechanics of an erythrocyte junctional complex in equibiaxial and anisotropic deformations

The erythrocyte membrane skeleton deforms constantly in circulation, but the mechanics of a junctional complex (JC) in the network is poorly understood. We previously proposed a 3-D mechanical model for a JC (Sung, L. A., and C. Vera. Protofilament and hexagon: A three-dimensional mechanical model for the junctional complex in the erythrocyte membrane skeleton. Ann Biomed Eng 31:1314-1326, 2003) and now developed a mathematical model to compute its equilibrium by dynamic relaxation. We simulated deformations of a single unit in the network to predict the tension of 6 alphabeta spectrin (Sp) (top, middle, and bottom pairs), and the attitude of the actin protofilament [pitch (theta), yaw (phi) and roll (psi) angles]. In equibiaxial deformation, 6 Sp would not begin their first round of "single domain unfolding in cluster" until the extension ratio (lambda) reach approximately 3.6, beyond the maximal sustainable lambda of approximately 2.67. Before Sp unfolds, the protofilament would gradually raise its pointed end away from the membrane, while phi and psi remain almost unchanged. In anisotropic deformation, protofilaments would remain tangent but swing and roll drastically at least once between lambda(i) = 1.0 and approximately 2.8, in a deformation angle- and lambda(i)-dependent fashion. This newly predicted nanomechanics in response to deformations may reveal functional roles previous unseen for a JC, and molecules associated with it, during erythrocyte circulation.

Fourier Transform Spectroscopy of Chemiluminescence from the SrO A(1)Sigma(+)-X(1)Sigma(+) Transition

The A(1)Sigma(+)-X(1)Sigma(+) chemiluminescence spectrum of SrO was observed using a Fourier transform spectrometer. SrO was produced in a Broida-type oven from the Sr + N(2)O reaction. A total of 75 bands from (88)SrO, (87)SrO, and (86)SrO were measured in the range of 7600-13 600 cm(-1) at a resolution of 0.04 cm(-1). The vibrational levels of the ground state were observed up to v" = 12 and over 10 000 rovibrational lines with J as high as 153 were analyzed at a precision of about 0.005 cm(-1). Significantly improved spectral constants for the ground state were obtained by representing the perturbed excited state by term values and by adding the known microwave data and infrared data to our fit. Strong perturbations were observed in the upper A state. The vibrational levels of the A(1)Sigma(+) state were measured up to v' = 8 and some new perturbations are reported. Copyright 2000 Academic Press.

Assessing the diet of adolescent girls in the UK

OBJECTIVE

To assess the ability of a food frequency questionnaire (FFQ1) and a food checklist (FCL) to determine energy and macronutrient intakes of adolescent girls in the general population.

DESIGN

Energy and macronutrient intakes determined by FFQ1 and the FCL were compared with those from a 7-day weighed dietary record (WDR). The reproducibility of FFQ1 was assessed by a comparison of intakes with those from a repeated questionnaire (FFQ2) completed a month later.

SETTING

Southampton, UK.

SUBJECTS

Forty-seven 15-year-old girls completed FFQ1 and the WDR and FCL; and 61 girls completed FFQ1 and FFQ2.

RESULTS

The broad dietary patterns described by the three methods of assessment were similar, although absolute intakes differed. Energy and macronutrient intakes determined by FFQ1 were higher than those recorded in the WDR (all P < 0.001), but intakes assessed by the FCL and WDR were similar. Only FFQ1-assessed energy intakes appeared consistent with predicted energy requirements. With the exception of protein intake, there was reasonable agreement between FFQ1 and the WDR in their estimation of energy and macronutrient intake (range of correlation coefficients 0.28 for energy to 0.33 for carbohydrate). The poorer agreement between FFQ1 and the WDR in their estimates of protein intake arose principally from the misclassification of meat and fish intake, although there was no obvious explanation for this. Energy and macronutrient intakes were similar for FFQ1 and FFQ2.

CONCLUSIONS

Adolescent girls give reproducible answers in response to a self-administered FFQ, which yield useful information about their broad dietary patterns. The FFQ may be a more suitable dietary assessment method than prospective records for use in general population studies of girls of this age. We discuss suggestions for its improved performance.

Abnormal surfactant composition and activity in severe bronchiolitis

A prospective study of infants under 1 y of age, ventilated for severe viral bronchiolitis, was carried out in four paediatric intensive care units in order to study surfactant activity and composition in this condition. Lung lavage fluid from 24 infants with bronchiolitis, 19 with bronchiolitis and sepsis or cardiac failure and 12 controls were analysed by the "click test" for surfactant activity and for phospholipids. Surfactant activity was present in all controls, but in only 2 of the 24 infants with bronchiolitis alone. The presence of phosphatidylglycerol correlated perfectly with the click test, suggesting that reduced activity is due to changes in surfactant lipid composition. In those with bronchiolitis plus coexisting disease, surfactant activity and phosphatidylglycerol were absent in only half. Surfactant activity and phosphatidylglycerol re-appeared by extubation. Severe viral bronchiolitis is associated with an absence of surfactant activity and PG, which resolves by clinical recovery. Infants with coexisting conditions are not always surfactant deficient. Surfactant administration is likely to be beneficial, but requires a selective approach.

Reference ranges for cardiac dimensions and blood flow velocity in preterm infants

AIM

To establish reference ranges for cardiac dimensions and Doppler measurements in preterm infants.

METHODS

79 infants of less than 34 weeks' gestation were examined by echocardiography on days 0, 7, and 28 after birth, to produce a set of reference ranges and to examine changes in these indices over the first month of life. The following dimensions were measured: interventricular septum, left ventricular posterior wall, left interventricular diameter at end systole and diastole, left atrium, and aortic root; Doppler measurements were made of maximum blood flow velocity (Vmax) through the pulmonary, aortic, mitral, and tricuspid valves.

RESULTS

Reference ranges are given. Cardiac dimensions correlated well with gestation and birth weight but Vmax did not. There was a significant increase in measurements over time. The "normal" preterm infant also appeared to often have asymmetrical septal hypertrophy. Antenatal dexamethasone administration did not appear to affect the measurements.

CONCLUSIONS

There is a close correlation with both gestation and birth weight for all physical measurements. Echocardiograms in preterm babies clearly differ from those in older children and adults.

Cardiac effects of short course dexamethasone in preterm infants

AIM

To examine the incidence and natural history of left ventricular hypertrophy (LVH) associated with the shorter 2-3 week course of dexamethasone, now more usual, for chronic lung disease.

METHOD

Thirty one infants, gestational age 23-34 (median 26) weeks, birthweight 500-2054 (median 815)g, received dexamethasone, starting at 0.4-0.6 mg/kg/day, at a median of 11 days of age (range 2-34), weaning over a period of 2-3 weeks. Eighteen preterm neonates were studied as controls over a similar time period. Serial echocardiographic measurements of end diastolic interventricular septum (IVSd) and left ventricular posterior wall (LVPWd) thicknesses were taken before, and up to 48 days after, starting dexamethasone. Maximum Doppler blood flow velocities from the left ventricular outflow tract (LVOT) were measured.

RESULTS

Left ventricular hypertrophy (LVH) occurred in 29 babies (94%). Median hypertrophy of the IVSd in those receiving dexamethasone was 67% and LVPWd 56% of baseline measurements, significantly greater than control infants (p < 0.001). LVH appeared by a median of three days, peaking by a median of 10 days. All resolved by a median of 27 days. LVOT obstruction was not seen. There was no significant correlation with birthweight, gestation, blood pressure, or glucose tolerance.

CONCLUSIONS

LVH developed in almost all preterm neonates receiving a 2-3 week course of dexamethasone, but was of little clinical importance and always resolved. Echocardiography is probably not required routinely in infants receiving such short course dexamethasone for chronic lung disease.

Factors affecting the neonatal response to artificial surfactant

OBJECTIVE

To define the individual neonatal response to the artificial surfactant, Exosurf, and factors that may influence the response.

METHODOLOGY

Eighty-two consecutive, preterm neonates with respiratory distress syndrome, who received Exosurf at < 12 h of age were studied. Their response was categorized from the graphical change in the oxygenation index with postnatal age, for 12 h after each of two doses of surfactant and assessed independently by two observers. Clinical factors were analysed for their effect on the four pre-defined categories of response, namely: none; mild; good: relapsed; and good: sustained.

RESULTS

Within the first 12 h, 11% of the neonatas showed no response, 5% a mild response and 84% a good response, but 34% relapsed. By 24 h, 6% still showed no response (all died), 11% showed a mild response and 83% a good response, of whom half relapsed. At 24 h, no response was significantly associated with low gestational age and asphyxia, mild response with less severe lung disease. According to the response there was a gradation in the risk of death during the first week.

CONCLUSIONS

The response to Exosurf can be individually and reproducibly categorized and demonstrated that 83% of neonates had a good response but half relapsed. No response was associated with extreme prematurity and asphyxia.

A blinded comparison of clinical and echocardiographic evaluation of the preterm infant for patent ductus arteriosus

The accuracy of the characteristic physical signs of a patent ductus arteriosus (PDA), that is, a systolic murmur, increased volume of pulses and increased praecordial activity, in diagnosing a haemodynamically significant PDA in ventilated premature infants was prospectively evaluated. Fifty-five ventilated preterm infants (birthweight < 1500 g) had daily echocardiographic and clinical evaluation for a PDA for the first 7 days of life. The examiners were blinded to each other's findings. Probability analysis was performed for the accuracy of each clinical sign in detecting a haemodynamically significant PDA as defined by echocardiographic criteria. Clinical signs were poor at detecting a significant PDA in the first 4 days of life. On day 1, none of the 10 infants with a significant PDA had a murmur. By day 4, clinical signs were better at detecting a significant PDA, but specificity remained poor with many false positive signs. Six infants had murmurs with a closed duct. The development of echocardiographic haemodynamic significance preceded the development of physical signs by a mean of 1.8 days. Significant ductal shunts often occurred silently, but the development of a murmur often marked an increase in the velocity of the flow through the duct rather than an increase in the size of a shunt. This study confirms that echocardiography is required for the reliable early diagnosis of a PDA in ventilated preterm infants.

"Click test": rapid diagnosis of the respiratory distress syndrome

Appropriate and early treatment with exogenous surfactant has clinical and economic benefits for neonates with pulmonary surfactant deficiency. In order to rapidly and reliably identify such neonates, we have evaluated the shake and click tests, biophysical tests of surfactant function, using 0.2 mL samples of tracheal (TA) and gastric aspirates (GA). Samples from 181 neonates with a gestational age range of 24-40 weeks were shaken with 95% ethanol. If bubbles formed (positive shake test) they were examined in air-free water under a microscope. In a positive shake or click test, the bubbles rhythmically increase and then decrease in size, denoting the presence of active surfactant. The probability of the tests to predict clinical surfactant deficiency was analyzed. The latter was defined as respiratory distress syndrome or transient tachypnea of the newborn diagnosed by chest radiography and clinical criteria. The click test on TA from preterm infants was most accurate, with a 100% positive predictive value and specificity, and a 93% and 94% negative predictive value and sensitivity respectively. These values for GA were 73%, 84%, 97%, and 95%, respectively. The test is quick, simple, inexpensive, reproducible, and unaffected by contamination with blood. The accuracy of this test on TA in diagnosing surfactant deficiency in neonates would permit early and optimal treatment with exogenous surfactant. When performed on GA, the test could aid decisions regarding transfer of neonates to tertiary level care.

Nursing and empowerment: concepts and strategies

This paper argues that although there has been an increasing use of the term 'empowerment' in the nursing literature, the word is sometimes employed uncritically and in inappropriate contexts. The origins of the expression in community development work are noted, in an effort to set the activity of empowerment in its political context and to discuss the implications of this for the relative power of health professionals and service users. A distinction is drawn between the meaning of the term at the individual and the community level and an outline strategy is discussed for nurses who may wish to think through what empowering patients or clients will entail.

Sinusitis-induced subdural empyema

Over a 17 year period, 1975-91, 10 children were managed who had sinusitis-induced subdural or extradural empyema. Their ages ranged from 6 to 14 years, with a mean of 11 years. All presented with worsening headaches, fever, vomiting, all had neurological abnormalities, and all had symptoms or signs suggestive of sinusitis. Initial computed tomography gave normal results in five cases and the empyema was diagnosed on the second or third scan. All patients had symptoms for at least one to two weeks before the diagnosis was made. Streptococcus milleri was the organism most frequently implicated. Medical treatment was started in all cases on admission, but all required surgical intervention before resolution.

HIV in the U.K.: problems of prevalence, sociological response and health education

It is argued that the prevalence of AIDS is substantially under-represented in existing national AIDS data. Thus although official statistics demonstrate significant recent shifts in transmission routes for HIV, health educators are faced with a problem because it is difficult to develop preventive strategies against a syndrome whose prevalence can only be estimated. Problems of the true extent of the prevalence of HIV are compounded when there is a lack of knowledge about the specifics of heterosexual behaviour. It is unwise to assume that the protective strategies developed by gay men in the face of HIV are routinely available for adoption by heterosexuals, who are characterised by social divisions of age, gender and relative amounts of social power. These concerns represent a problem for health educators. To date, sociological work may not have made the most effective contribution in its support of intervention strategies against HIV/AIDS. Examination of the empirical literature on lay concepts of health and illness reveals a pessimistic stance on the part of some researchers about the ability of individuals to modify behaviour. More positive readings of their own data are possible. The traditional concerns to emphasise the socio-economic determinants of health and behaviour, now also shared by some health educators, should not obscure a concern for the fate of individuals. The most effective contribution that health promotion may be able to make to the control of HIV in the heterosexual population is to assist in the development of strategies of empowerment and 'horizontal intervention'.

Understanding Matte-Blanco

Matte-Blanco claims to explain a wide range of characteristics of the Unconscious from a simple base. His theory of the logic of the Unconscious is based on two principles: first, that the Unconscious treats every class as a subclass of a more general class. Second, that the Unconscious treats relations as reversible. It is claimed that it is possible to explain such a wide range of characteristics of the Unconscious because these two principles contradict one another. From the theory of formal systems we know that any theory with contradictory principles explains everything and so explains very little.

Behavioral methods for inferring anatomical linkage between rewarding brain stimulation sites

Rats lever pressed for concurrent electrical stimulation of the lateral hypothalamus and ventral tegmentum. The pulse-pair stimulation technique was used, with the first pulse of each pair applied to one electrode and the second to the other electrode; the intrapair interval was varied. The effectiveness of stimulation, measured behaviorally, increased abruptly (within .4 msec) as the intrapair interval was increased in the range from 1.0 to 2.0 msec. These results, which do not resemble single-electrode refractory period results, are interpreted as evidence of collision in the directly stimulated, reward-related neurons linking the two sites. We conclude that self-stimulation of the medial forebrain bundle involves the direct activation of long-axon, longitudinal pathways. Estimates of the conduction velocity in the fibers subserving the collision-like effects are consistent with the properties of small myelinated axons but not central monoaminergic fibers.

Kindling-related changes in afterdischarge "thresholds"

Amygdaloid stimulations were applied to rats at gradually increasing current intensities once every 60 sec until and afterdischarge (AD) was recorded through the stimulation electrode. These initial AD "thresholds" (x = 75 muA) were reduced over a 4-day period by a series of 12 subthreshold stimulations. In contrast, stimulations administered on the same regimen but at a higher intensity (400 muA) had raised the AD threshold. The decreases in the AD threshold were relatively permanent, whereas the elevated thresholds were subsequently reduced to control levels by a series of subthreshold stimulations or by a 7-day stimulation-free period. Two days following the completion of Experiment 1, all of the rats were injected with a low dose of pentylenetetrazol. The incidence of pentylenetetrazol-induced epileptic symptoms was much higher in the experimental animals than in the control subjects previously subjected only to the threshold estimation procedure.