Systematic ab initio study of the compressibility of silicate garnets

The structural properties of the silicate garnets andradite, Ca(3)Fe(2)Si(3)O(12), uvarovite, Ca(3)Cr(2)Si(3)O(12), knorringite, Mg(3)Cr(2)Si(3)O(12), goldmanite, Ca(3)V(2)Si(3)O(12), blythite, Mn(2+)(3)Mn(3+)(2)Si(3)O(12), skiagite, Fe(2+)(3)Fe(3+)(2)Si(3)O(12), calderite, Mn(2+)(3)Fe(3+)(2)Si(3)O(12), and khoharite, Mg(3)Fe(3+)(2)Si(3)O(12), have been investigated with a quantum-mechanical model as a function of applied pressure. The study has been performed with the density functional theory code CASTEP, which uses pseudopotentials and a plane-wave basis set. All structural parameters have been optimized. The calculated static geometries (cell parameters, internal coordinates of atoms and bond lengths), bulk moduli and their pressure derivatives are in good agreement with the experimental data available. Predictions are made for those cases where no experimental data have been reported. The data clearly indicate that the elastic properties of all silicate garnets are dominated by the compressibility of the dodecahedral site. The compression mechanism is found to be based on a bending of the angle between the centers of the SiO(4) tetrahedra and the adjacent octahedra, as in the aluminosilicate garnets. An analysis of the relationship between ionic radii of the cations and the compressibility of silicate garnets is presented.

Unified optimization criterion for energy converters

We propose a unified optimization criterion for energy converters. It represents the best compromise between energy benefits and losses for a specific job and neither an explicit evaluation of entropies nor the consideration of environmental parameters are required. For all considered systems the criterion predicts a performance regime laying between those of maximum efficiency and maximum useful energy. Such regime has been invoked as optimum not only in macroscopic heat engines but also in some molecular motors.

Structural properties of lanthanide and actinide compounds within the plane wave pseudopotential approach

We show that plane wave ultrasoft pseudopotential methods readily extend to the calculation of the structural properties of lanthanide and actinide containing compounds. This is demonstrated through a series of calculations performed on UO, UO2, UO3, U3O8, UC2, alpha-CeC2, CeB6, CeSe, CeO2, NdB6, TmOI, LaBi, LaTiO3, YbO, and elemental Lu.

Nonhypoglycemic drug reactions of agents used to treat diabetes

The different classes of agents now available for the treatment of diabetes, each with its own unique mechanism of action, present the clinician with numerous choices to achieve glycemic control. Therapy can be tailored for each patient. If the primary problem is insulin resistance, a thiazolidinedione can be used. The clinician should remember the potential adverse reactions of the drugs and their potential interaction with other conditions a patient may have. After this careful consideration, the optimal therapeutic regimen for a patient can be developed.

A new set of Arabidopsis expressed sequence tags from developing seeds. The metabolic pathway from carbohydrates to seed oil

Large-scale single-pass sequencing of cDNAs from different plants has provided an extensive reservoir for the cloning of genes, the evaluation of tissue-specific gene expression, markers for map-based cloning, and the annotation of genomic sequences. Although as of January 2000 GenBank contained over 220,000 entries of expressed sequence tags (ESTs) from plants, most publicly available plant ESTs are derived from vegetative tissues and relatively few ESTs are specifically derived from developing seeds. However, important morphogenetic processes are exclusively associated with seed and embryo development and the metabolism of seeds is tailored toward the accumulation of economically valuable storage compounds such as oil. Here we describe a new set of ESTs from Arabidopsis, which has been derived from 5- to 13-d-old immature seeds. Close to 28,000 cDNAs have been screened by DNA/DNA hybridization and approximately 10,500 new Arabidopsis ESTs have been generated and analyzed using different bioinformatics tools. Approximately 40% of the ESTs currently have no match in dbEST, suggesting many represent mRNAs derived from genes that are specifically expressed in seeds. Although these data can be mined with many different biological questions in mind, this study emphasizes the import of photosynthate into developing embryos, its conversion into seed oil, and the regulation of this pathway.

Equivalence of two approaches for the inhomogeneous density in the canonical ensemble

In this Brief Report we show that the inhomogeneous density obtained from a density-functional theory of classical fluids in the canonical ensemble (CE), recently presented by White et al. [Phys. Rev. Lett. 84, 1220 (2000)], is equivalent to first order to the result of the series expansion of the CE inhomogeneous density introduced by Gonzalez et al. [Phys. Rev. Lett. 79, 2466 (1997)].

Video-assisted cardioscopy for intraventricular repair in congenital heart disease

BACKGROUND

Video-assisted thoracoscopic surgical techniques have been widely adopted as a means to reduce surgical trauma. By adapting pediatric thoracoscopic instrumentation, we have developed a technique for video-assisted cardioscopy (VAC). We report our experience and describe the technical feasibility of VAC.

METHODS

Since June 1995, 409 consecutive patients underwent 431 intracardiac procedures (ventricular septal defect, 150; tetralogy of Fallot or double outlet right ventricle, 101; atrioventricular canal, 52; subaortic stenosis, 43; valve repair, 50; Rastelli procedure, 12; Konno or Ross Konno operation, 11; and miscellaneous, 12) using VAC at Miami Children's Hospital. Using a prospective database, we tracked outcomes and operative events to delineate the usefulness and efficacy of this technique.

RESULTS

VAC provided clear and precise imaging of small or remote intracardiac structures during repair of congenital heart defects without technical complications. Procedure times and aortic cross-clamp times using VAC were not prolonged. Intraoperative images were collected for every operation, documenting each patient's cardiac anatomy before and after repair. Surgery through small incisions was facilitated. Operative mortality was 1.2% (5 of 409), and no patient required reoperation before discharge. At a mean follow-up interval of 22 months, the incidence of reoperation for residual or recurrent lesions was 1.2% (5 of 404).

CONCLUSIONS

Our experience demonstrates the technical feasibility and clinical utility of routine endoscopic imaging during open heart surgery for congenital heart repair.

Preliminary validation of a short-term morphological assay to evaluate adverse effects on amphibian metamorphosis and thyroid function using Xenopus laevis

Short-term static-renewal studies were performed on Xenopus laevis embryos with 16 selected test materials from day 50 (stage 60) to day 64 (stage 66) (14-day test) to evaluate effects on tail resorption and thyroid function. Of the 16 test materials, nine were found to inhibit significantly the rate of tail resorption, four were found to stimulate metamorphosis and three had no appreciable effect on the rate of metamorphosis. In an effort to determine if the morphological effects observed were related to alteration in thyroid activity, measurement of triiodothyronine (T3) in the test organisms and coadministration studies using thyroxine (agonist) or propylthiouracil (antagonist) were performed based on the morphological response noted during tail resorption. Of the nine compounds found to inhibit the rate of tail resorption, six were found to reduce the levels of T3. In each case, the inhibitory response could be at least partially alleviated by the co-administration of thyroxine. Larvae exposed to the four stimulatory agents had somewhat elevated levels of T3 and were responsive to propylthiouracil antagonism. These results suggest that 12 of the 14 compounds tested in this study that altered the rate of tail resorption did so via the thyroid axis. Overall, the X. laevis model appeared to be a suitable system for evaluating the impact of environmental agents and chemical products on thyroid function.

Networks of interneurons with fast and slow gamma-aminobutyric acid type A (GABAA) kinetics provide substrate for mixed gamma-theta rhythm

During active exploration, hippocampal neurons exhibit nested rhythmic activity at theta ( approximately 8 Hz) and gamma ( approximately 40 Hz) frequencies. Gamma rhythms may be generated locally by interactions within a class of interneurons mediating fast GABA(A) (GABA(A,fast)) inhibitory postsynaptic currents (IPSCs), whereas theta rhythms traditionally are thought to be imposed extrinsically. However, the hippocampus contains slow biophysical mechanisms that may contribute to the theta rhythm, either as a resonance activated by extrinsic input or as a purely local phenomenon. For example, region CA1 of the hippocampus contains a slower class of GABA(A) (GABA(A,slow)) synapses, believed to be generated by a distinct group of interneurons. Recent evidence indicates that these GABA(A,slow) interneurons project to the GABA(A, fast) interneurons that contribute to hippocampal gamma rhythms. Here, we use biophysically based simulations to explore the possible ramifications of interneuronal circuits containing separate classes of GABA(A,fast) and GABA(A,slow) interneurons. Simulated interneuronal networks with fast and slow synaptic kinetics can generate mixed theta-gamma rhythmicity under restricted conditions, including strong connections among each population, weaker connections between the two populations, and homogeneity of cellular properties and drive. Under a broader range of conditions, including heterogeneity, the networks can amplify and resynchronize phasic responses to weak phase-dispersed external drive at theta frequencies to either GABA(A,slow) or GABA(A,fast) cells. GABA(A, slow) synapses are necessary for this process of amplification and resynchronization.

Isolated bypass grafting of the left internal thoracic artery to the left anterior descending coronary artery: late consequences of incomplete revascularization

OBJECTIVE

Multiple strategies to achieve some degree of myocardial revascularization are available. In some, less complete revascularization is accepted to limit invasiveness. To examine the issues of incomplete revascularization, we assessed the long-term impact of additional non-left anterior descending coronary artery stenoses in patients undergoing only grafting of the left internal thoracic artery to the left anterior descending coronary artery.

METHODS

A total of 2067 patients underwent primary isolated grafting of the left internal thoracic artery to the left anterior descending coronary artery from 1971 to 1997. Of these, 26% and 13% had 2- and 3-system disease, respectively. Multivariable analyses of survival and reintervention were performed in the hazard function domain for 27,683 patient-years of follow-up (mean 14 +/- 6.7).

RESULTS

Survival was 99%, 88%, and 62% at 1, 10, and 20 years. Right coronary artery or left circumflex system disease of 50% or more (P =.02) and particularly high-grade (>/=70%) left circumflex (P =.01) and proximal right coronary artery disease (P =.01), as well as any degree of left main trunk stenosis (P <.0001), were associated with reduced long-term survival. Compared with 75% 20-year survival in patients with no non-left anterior descending disease, those with either left circumflex or left main trunk disease experienced a 44% survival, and those with proximal right coronary artery disease, 42%. The most common stated reason for incomplete revascularization was small vessel size. Freedom from reintervention was 89% and 65% at 10 and 20 years, respectively. High-grade left main trunk disease, but, in contrast, mid or distal disease of the right coronary artery, and not left circumflex disease, were risk factors for reintervention.

CONCLUSIONS

These findings call into question the long-term appropriateness of interventions whose strategy includes leaving unrevascularized segments in territories not in the distribution of the left anterior descending coronary artery.

Hybrid finite element-finite difference method for thermal analysis of blood vessels

A hybrid finite-difference/finite-element technique for the thermal analysis of blood vessels embedded in perfused tissue has been developed and evaluated. This method provides efficient and accurate solutions to the conjugated heat transfer problem of convection by blood coupled to conduction in the tissue. The technique uses a previously developed 3D automatic meshing method for creating a finite element mesh in the tissue surrounding the vessels, coupled iteratively with a 1-D marching finite difference method for the interior of the vessels. This hybrid technique retains the flexibility and ease of automated finite-element meshing techniques for modelling the complex geometry of blood vessels and irregularly shaped tissues, and speeds the solution time by using a simple finite-difference method to calculate the bulk mean temperatures within all blood vessels. The use of the 1D finite-difference technique in the blood vessels also eliminates the large computer memory requirements needed to accurately solve large vessel network problems when fine FE meshes are used in the interior of vessels. The accuracy of the hybrid technique has been verified against previously verified numerical solutions. In summary, the hybrid technique combines the accuracy and flexibility found in automated finite-element techniques, with the speed and reduction of computational memory requirements associated with the 1D finite-difference technique, something which has not been done before. This method, thus, has the potential to provide accurate, flexible and relatively fast solutions for the thermal analysis of coupled perfusion/blood vessel problems, and large vessel network problems.

Identification of the human cytochrome P450, P450RAI-2, which is predominantly expressed in the adult cerebellum and is responsible for all-trans-retinoic acid metabolism

Retinoids, particularly all-trans-retinoic acid (RA), are potent regulators of cell differentiation, cell proliferation, and apoptosis. The role of all-trans-RA during development and in the maintenance of adult tissues has been well established. The control of all-trans-RA levels in cells and tissues is regulated by the balance between its biosynthesis and its catabolism to inactive metabolites. The cytochrome P450 enzyme P450RAI (herein renamed P450RAI-1) is partially responsible for this inactivation of all-trans-RA. In this report, we describe the identification, molecular cloning, and characterization of a second related enzyme, P450RAI-2, which is also involved in the specific inactivation of all-trans-RA. Transiently transfected P450RAI-2 can convert all-trans-RA to more polar metabolites including 4-oxo-, 4-OH-, and 18-OH-all-trans-RA. Competition experiments with other retinoids suggest that all-trans-RA is the preferred substrate. The high level of expression of P450RAI-2, particularly in the cerebellum and pons of human adult brain, suggests a unique role for this enzyme in the protection of specific tissues from exposure to retinoids.

Heparin-coated cardiopulmonary bypass circuit: clinical effects in pediatric cardiac surgery

OBJECTIVES

Heparin-coated cardiopulmonary bypass (CPB) circuits have been reported to reduce complement activation and the inflammatory response associated with CPB. We retrospectively compared patients utilizing heparin-coated perfusion circuits with those using noncoated circuits to determine the clinical effects of the different circuits in pediatric cardiac surgery.

METHODS

Between July 1995 and July 1997, 203 patients weighing < 10 kg underwent cardiac surgery, 153 patients using heparin-coated bypass circuits and 50 patients using noncoated circuits. The 50 patients operated on with the noncoated circuit (Group N) were matched to 100 patients operated on with coated circuits (Group H) in age, weight, and type of procedure. Urine output during bypass, blood products used after bypass, postoperative ventilation days, hospital stay, morbidity, and mortality were compared between these groups.

RESULTS

Body weight, perfusion time, and procedure time were not different between the two groups. Urine output during bypass was notably greater in Group H than in Group N (11.3 +/- 10.5 mL/kg per hour vs 4.8 +/- 3.1 mL/kg per hour, respectively, p < 0.0001). Postoperative mechanical ventilation markedly decreased in Group H (Group H vs N = 2.8 +/- 2.7 days vs 5.1 +/- 7.5 days, respectively, p < 0.05). Red blood cell usage, hospital stay, morbidity, and mortality were not statistically different, although there was a tendency toward decreased transfusion of red cell and platelets in Group H (Group H vs N = 61.2 +/- 121.1 mL/kg vs 102.0 +/- 176.7 mL/kg, respectively, in red cell, p = 0.15; and Group H vs N = 7.9 +/- 13.7 mL/kg vs 13.2 +/- 24.5 mL/kg, respectively, in platelets, p = 0.16).

CONCLUSIONS

Patients operated on with the use of heparin-coated circuits had increased urine output during bypass and required less time postoperatively on the ventilator. These results suggest a reduction in the acute inflammatory response, capillary leakage, and overall systemic edema. We now routinely use coated circuits on all pediatric pump cases.

Minimally invasive resection of congenital subaortic stenosis

Fifteen consecutive patients with membranous subaortic stenosis underwent resection by a minimal-access approach through a partial upper sternotomy using a cardioscope. There were no operative deaths and no postoperative complications. Twelve patients (80%) were extubated in the operating room. The mean hospital stay was 3.1 days, and 3 patients (20%) needed blood products. Our experience demonstrates that this modified approach is a safe and effective surgical option for resection of subaortic stenosis.

Acute injury incidence in professional county club cricket players (1985-1995)

BACKGROUND

There is a dearth of evidenced based research into sports injury in professional cricket.

AIM

To investigate the incidence, nature, and site of acute injuries sustained by professional cricketers at one English county club over the period 1985-1995.

METHODS

Injuries in a sample of 54 cricketers who had played in the first team for the same county cricket club in any or all seasons between 1985 and 1995 were investigated. Injury was defined as the onset of pain or a disability resulting from either training for or playing cricket, which caused the player to seek medical attention.

RESULTS

An acute injury rate of 57.4 injuries per 1000 days of cricket played was found, with most injuries sustained during April, the month in which the least number of days were played. The lower limb was the region most vulnerable to injury, accounting for 44.9% of all injuries, followed by the upper limb (29.4%), the trunk (20.0%), and the head and neck (5.7%). No significant difference in injury incidence among player positions was found.

CONCLUSION

There is a need for a system of epidemiological data collection and development of a national cricket injury database to help predict, reduce, and prevent injury at all levels of the game.

An accurate, convective energy equation based automated meshing technique for analysis of blood vessels and tissues

An automated three-element meshing method for generating finite element based models for the accurate thermal analysis of blood vessels imbedded in tissue has been developed and evaluated. The meshing method places eight noded hexahedral elements inside the vessels where advective flows exist, and four noded tetrahedral elements in the surrounding tissue. The higher order hexahedrals are used where advective flow fields occur, since high accuracy is required and effective upwinding algorithms exist. Tetrahedral elements are placed in the remaining tissue region, since they are computationally more efficient and existing automatic tetrahedral mesh generators can be used. Five noded pyramid elements connect the hexahedrals and tetrahedrals. A convective energy equation (CEE) based finite element algorithm solves for the temperature distributions in the flowing blood, while a finite element formulation of a generalized conduction equation is used in the surrounding tissue. Use of the CEE allows accurate solutions to be obtained without the necessity of assuming ad hoc values for heat transfer coefficients. Comparisons of the predictions of the three-element model to analytical solutions show that the three-element model accurately simulates temperature fields. Energy balance checks show that the three-element model has small, acceptable errors. In summary, this method provides an accurate, automatic finite element gridding procedure for thermal analysis of irregularly shaped tissue regions that contain important blood vessels. At present, the models so generated are relatively large (in order to obtain accurate results) and are, thus, best used for providing accurate reference values for checking other approximate formulations to complicated, conjugated blood heat transfer problems.

The Ross operation in a Jehovah's Witness: a paradigm for heart surgery in children without transfusion

A 3-year-old 18 kg male child of the Jehovah's Witness faith presented with severe aortic regurgitation. A successful Ross procedure was performed using a pulmonary autograft, without the use of blood or blood product transfusion. Blood conservation strategy included: (1) preoperative treatment with recombinant human erythropoietin; (2) intraoperative strategies, including technical modifications to the Ross procedure, and the prophylactic use of fibrin glue; (3) utilization of a heparin-bonded cardiopulmonary bypass circuit and assisted venous drainage; and 4) the use of prebypass phlebotomy, cell-saving device and autotransfusion. The patient was discharged home on postoperative day 7 with a hemoglobin level of 11.9.

Channel noise in neurons

The probabilistic gating of voltage-dependent ion channels is a source of electrical 'channel noise' in neurons. This noise has long been implicated in limiting the reliability (repeatability) of neuronal responses to repeated presentations of identical stimuli. More recently, it has been shown to increase the range of spiking behaviors exhibited in some neural populations. Channel numbers are tied to metabolic efficiency and the stability of resting potential, and channel noise might be exploited by future cochlear implants in order to improve the temporal representation of sound.

Cosgrove-Edwards Annuloplasty System: midterm results

BACKGROUND

The Cosgrove-Edwards Annuloplasty System includes a universally flexible band that corrects mitral annular dilatation via measured plication of the posterior annulus. The purpose of this study was to evaluate midterm clinical and functional results in the first 197 patients receiving this flexible annuloplasty band at mitral valve repair.

METHODS

From February 1993 to July 1994, 197 consecutive patients with mitral regurgitation had mitral valve repair using this system. Valve disease was degenerative in 73%, rheumatic in 15%, ischemic in 5%, infectious in 2.5%, and other in 4%.

RESULTS

Immediately after repair, echocardiographic mitral regurgitation was none or trivial in 92%, 1+ in 5%, and 2+ in 3%. There were no hospital deaths. Late follow-up was available in 195 patients (99%), with 661 patient-years of follow-up available for analysis. Four-year actuarial survival was 93%, freedom from thromboembolism 94%, from endocarditis 98%, and from reoperation 95%. At a mean interval of 18 months, echocardiography in 157 patients demonstrated no or trace mitral regurgitation in 56%, 1+ in 24%, 2+ in 9%, 3+ in 6%, and 4+ in 3%. At a mean of 61 +/- 5 months, reconstruction of the mitral annulus from real-time three-dimensional echocardiographic images in 10 patients confirmed preserved nonplanar shape and sphincter mechanism of the mitral annulus. Annular orifice area decreased 28% +/- 11% during the cardiac cycle from a mean of 10.1 +/- 3.9 cm2 in diastole to 7.2 +/- 2.8 cm2 in systole.

CONCLUSIONS

This annuloplasty system is effective for repair of mitral regurgitation secondary to all causes and preserves mitral annular flexibility and function at 5-year follow-up.

Pattern of degeneration of the spiral ganglion cell and its processes in the C57BL/6J mouse

Although degeneration of spiral ganglion cells has been described as a histopathologic correlate of hearing loss both in animals and humans, the pattern and sequence of this degeneration remain controversial. Degeneration of hair cells and of spiral ganglion cells and their dendritic processes was evaluated in the C57BL/6J mouse, in which there is a genetically determined progressive sensorineural loss starting in the high frequencies that is similar to the pattern commonly seen in the human. Auditory function was evaluated by brainstem evoked responses, and degeneration of hair cells, ganglion cells and their dendrites was evaluated histologically at 3, 8, 12 and 18 months of age. Progressive loss of auditory sensitivity was correlated with the loss of outer and inner hair cells and spiral ganglion cells and their dendritic processes. In addition, dendritic counts were consistently lower at a distal location in the osseous spiral lamina (i.e. near the organ of Corti) than at a proximal location (i.e. near the spiral ganglion), and the difference between the number of distal dendrites and the number of proximal dendrites tended to be greater with advancing age. These observations suggest an age-related progressive retrograde degeneration of spiral ganglion cells. Thus, in degenerating cochleas, some remaining spiral ganglion cells may have no distal dendritic processes near the organ of Corti. This may have implications for successful stimulation of the cochlear neuron in cochlear implantation.

Density-functional theory of inhomogeneous fluids in the canonical ensemble

We present a density-functional approach for dealing with inhomogeneous fluids in the canonical ensemble. A general relation is proposed between the free-energy functionals in the canonical and the grand canonical ensembles. The minimization of the canonical-ensemble free-energy functional gives rise to Euler-Lagrange equations which involve averaged Ornstein-Zernike equations of second and third order. The theory is especially appropriate for systems with a small, fixed number of particles. As an example of application we obtain accurate results for the density profile of a hard-sphere fluid in a closed spherical cavity that contains only a few particles.