Tracing the phase diagram of the four-site water potential (TIP4P)

We present here the phase diagram for one of the most popular water models, the four-point transferable intermolecular potential (TIP4P) model. We show that TIP4P model, does indeed provide a qualitatively correct description of the phase diagram of water. The melting line of the five-point transferable intermolecular potential (TIP5P) at low pressures is also presented.

Phase diagram of water from computer simulation

The phase diagram of water as obtained from computer simulations is presented for the first time for two of the most popular models of water, TIP4P and SPC/E. This Letter shows that the prediction of the phase diagram is an extremely stringent test for any water potential function, and that it may be useful in developing improved potentials. The TIP4P model provides a qualitatively correct description of the phase diagram, unlike the SPC/E model which fails in this purpose. New behavior not yet observed experimentally is predicted by the simulations: the existence of metastable reentrant behavior in the melting curves of the low density ices (I,III,V) such that it could be possible to transform them into amorphous phases by adequate changes in pressure.

Computer simulation study of the global phase behavior of linear rigid Lennard-Jones chain molecules: Comparison with flexible models

The global phase behavior (i.e., vapor-liquid and fluid-solid equilibria) of rigid linear Lennard-Jones (LJ) chain molecules is studied. The phase diagrams for three-center and five-center rigid model molecules are obtained by computer simulation. The segment-segment bond lengths are L = sigma, so that models of tangent monomers are considered in this study. The vapor-liquid equilibrium conditions are obtained using the Gibbs ensemble Monte Carlo method and by performing isobaric-isothermal NPT calculations at zero pressure. The phase envelopes and critical conditions are compared with those of flexible LJ molecules of tangent segments. An increase in the critical temperature of linear rigid chains with respect to their flexible counterparts is observed. In the limit of infinitely long chains the critical temperature of linear rigid LJ chains of tangent segments seems to be higher than that of flexible LJ chains. The solid-fluid equilibrium is obtained by Gibbs-Duhem integration, and by performing NPT simulations at zero pressure. A stabilization of the solid phase, an increase in the triple-point temperature, and a widening of the transition region are observed for linear rigid chains when compared to flexible chains with the same number of segments. The triple-point temperature of linear rigid LJ chains increases dramatically with chain length. The results of this work suggest that the fluid-vapor transition could be metastable with respect to the fluid-solid transition for chains with more than six LJ monomer units.

A new successful therapy for fetal chylothorax by intrapleural injection of maternal blood

We present two cases of fetal chylothorax and hydrops diagnosed at 20 weeks' gestation, both of which underwent successful intrauterine treatment. In Case 1, a transient, near total resolution began 2 weeks after an iatrogenic hemothorax following a second thoracocentesis performed at 24 + 6 weeks. Because of pleural fluid reaccumulation, a Cesarean section was performed at 36 weeks. The 3805-g female neonate was admitted to neonatal intensive care but was discharged 50 days later in a healthy condition. In Case 2, resolution occurred after a third thoracocentesis and a second pleural injection of maternal blood, performed at 26 weeks. A 2660-g female neonate was delivered vaginally at 38 weeks. The infant remained asymptomatic and was discharged aged 4 days. Our experience suggests a possible useful role of intrapleural blood injection for the treatment of fetal chylothorax.

Glutamate agonists release excitatory aminoacids from rat astrocytes

Astrocytes release glutamate (Glu) by the mobilisation of intracellular concentrations of Ca++. The rationale of the present work was to test whether Glu and its agonists, known to affect intracellular Ca++ content via the activation of metabotropic and ionotropic receptors, could modulate the astrocytic release of excitatory aminoacids. NMR experiments showed that Glu released uniformly labelled [13C] Glu in the incubation medium of rat astrocytes in primary cultures. Further experiments confirmed this finding and showed that the incubation of these cells with agonists and antagonists of Glu ionotropic and metabotropic receptors, produced a different modulation of Glu and aspartate release. The observed activations of the various receptors suggest a complex modulation of the release of the excitatory aminoacids. Such a release of is interpreted in terms of metabolic microzonation.

Isotropic-nematic phase transition: Influence of intramolecular flexibility using a fused hard sphere model

The role of flexibility on the liquid crystal isotropic-nematic phase transition has been studied by means of Monte Carlo simulation. We present equations of state for the isotropic-nematic branches and, in the isotropic phase, numerically calculated values for the virial coefficients B2, B3, and B4. We have studied two models: 11 hard sphere monomers fused in a linear configuration with a reduced bond length of 0.6 and a 15-monomer version of this model in which monomers at one end of the chain become flexible. We have observed spontaneous nematic liquid crystal formation for both of the fully rigid models, and also for models with up to six flexible monomers in the tail. We conclude that molecular flexibility has a strongly destabilizing effect on the nematic phase. This is probably due to the decrease in shape anisotropy that flexible tails allow.

Order-disorder transition in the solid phase of a charged hard sphere model

We investigate the solid phases of the restricted primitive model (RPM). Monte Carlo simulations show the existence of an order-disorder transition from a substitutionally disordered face centered cubic lattice (fcc) to a new ordered fcc structure which is proposed as the ground state of the RPM at the close packing density. Our results suggest that the new phase might turn out in a new triple point in the RPM phase diagram involving three solid phases: CsCl, fcc ordered and fcc disordered structures. The order-disorder transition is also studied using the cell theory. The theory shows good agreement with the simulation results and suggests that the transition is weakly first order.

The role of matching menstrual data with hormonal measurements in evaluating effectiveness of postcoital contraception

The effectiveness of postcoital contraception can only be estimated. The most commonly used method of calculation compares the expected pregnancy rate in the exposed population to the resultant pregnancies after treatment. Estimation of the fertile period and the day of ovulation are critical to calculate the expected pregnancies. The aim of this study was to improve the accuracy of calculations by evaluating the hormonal status on the day of contraceptive treatment. A total of 483 consecutive women requesting postcoital contraception was included in a prospective observational trial. A blood sample was obtained at the moment of consultation to measure serum luteinizing hormone, estradiol, and progesterone concentrations. An ethinylestradiol-levonorgestrel combination (100 micrograms/500 mg for two doses, 12 h apart) was then prescribed. The fertile period was estimated according to previous hormonal studies in the normal cycling population. Of 483 women, 64 (13.25%) women were excluded because they presented irregular menstrual cycles and 37 (7.6%) women were lost to follow-up. Two pregnancies occurred in the remaining 382 women. Following Wilcox's and Trussell's methods, 21.1 and 17.75 pregnancies should be expected, yielding an overall treatment effectiveness of 90.52% (95% confidence interval [CI] 62.58%-97.6%) and 88.73% (95% CI 55.93%-97.12%), respectively. Hormonal data were available in 356 women; 303 of whom presented with regular cycles. Hormonal information in this group restricted the number of exposed cases to 88 women. Of the women included in Trussell's method of analysis, only 51 (51.5%; p < 0.05) were at risk using hormonal data. Fifty-six percent (95% CI 34.9%-75.6%) of women with luteinizing hormone levels > 20 IU/L were not between days-1 and +1 of the cycle. Hormonal studies suggest that methods based on pregnancy risk calculated by cycle day do not faithfully reflect the real exposure.

Hepato-biliary abnormalities secondary to ceftriaxone use: a case report

Ceftriaxone was approved in 1997 for the treatment of otitis media despite previous studies that documented an association of ceftriaxone with elevated hepato-biliary enzymes and transient biliary stasis. The case cited here highlights the need for continued awareness education for physicians who may use ceftriaxone to treat common illnesses such as acute exudative tonsillitis and otitis media in children. Specifically, for children with a family history of gallbladder, biliary tract, liver or pancreas dysfunction, ceftriaxone may not be the drug of choice since the likelihood of complications is increased in this population. Additionally, ceftriaxone may cause problems in either adults or children with preexisting disease, who may not be well-nourished, or who may be dehydrated.

On the reaction mechanism of class Pi glutathione S-transferase

Theoretical calculations were performed to examine the ionization of the phenolic group of Tyr7 and the thiol group of glutathione in aqueous solution and in the protein class-pi glutathione S-transferase (GST-Pi). Three model systems were considered for simulations in the protein environments the free enzyme, the complex between glutathione and the enzyme, and the complex between 1-chloro-2.4-dinitrobenzene, glutathione, and the enzyme. The structures derived from Molecular Dynamics simulations were compared with the crystallographic data available for the complex between the inhibitor S-(p-nitrobenzyl)glutathione and GST-Pi, the glutathione-bound form of GST-Pi, and the free enzyme carboxymethylated in Cys47. Free-energy perturbation techniques were used to determine the thermodynamics quantities for ionization of the phenol and thiol groups. The functional implications of Tyr7 in the activation of the glutathione thiol group are discussed in the light of present results, which in agreement with previous studies suggest that Tyr7 in un-ionized form contributes to the catalytic process of glutathione S-transferase, the thiolate anion being stabilized by hydrogen bond with Tyr7 and by interactions with hydrating water molecules.

Pyrogens specifically disrupt the acquisition of a task involving cognitive processing in the rat

In addition to changes in body temperature and other metabolic and physiological responses corresponding to immune activation, pyrogens can induce profound behavioral changes referred to collectively as sickness behavior. One feature of sickness behavior, sometimes reported in clinical settings, but rarely exposed to experimental analysis, is depressed cognitive functioning. The present series of five experiments sought to demonstrate the existence of specific cognitive deficits in rats, independently of any confounding performance effects of pyrogen injections. The behavioral task used, called autoshaping, consisted of presenting hungry Wistar rats with a stimulus (introduction of a retractable lever) that predicted food delivery. Control rats quickly learned to press the lever, although this response does not influence the probability of food delivery. When pyrogens (250 micrograms/kg lipopolysaccharide, 4 micrograms/rat interleukin-1 beta, or 300 mg/rat yeast) were injected to rats during acquisition of this task, they severely disrupted acquisition while the pyrogen was active. The same treatments were, however, without effect on performance when injected later, when performance had stabilized. It is argued that these results demonstrate specific, performance-independent effects of pyrogens on the cognitive processes needed for the acquisition of this task. The results are discussed in terms of the relationship between these effects and the cytokines induced in the brain by pyrogens, and in terms of the exact nature of the cognitive process likely to be affected.

Increased sensitivity to triiodothyronine (T3) of broiler lines with a high susceptibility for ascites

1. In the studies reported here, broiler lines divergently selected for susceptibility to ascites under low temperature conditions were tested for their sensitivity to 3,3',5-triiodothyronine (T3) with respect to growth rate, rate of mortality, plasma concentrations of T3, right ventricular hypertrophy (RVH) and incidence of ascites. 2. Mean body weight of the ascites-susceptible line (BC-line) was higher than that of the ascites-resistant line (A-line). Adding 0.5 mg T3/kg of the diet depressed growth rate to the same extent in both lines. The effect of T3 on growth was more pronounced for males than for females. 3. T3-supplementation increased the relative weight of the heart and the incidence of RVH to the same extent in both lines. More of the T3-treated BC-line chickens had fluid accumulation in the abdominal cavity than the T3-treated A-line chickens. 4. Dietary T3-treatment depressed the plasma concentration of growth hormone (GH) profoundly and insulin-like growth factor (IGF-I) slightly but to the same extent in both lines. The coefficient of variation of GH concentrations indicate that T3 treatment mainly decreased GH-pulsatility in young growing broilers. 5. Higher doses of dietary T3 (1 and 2 mg/kg) increased mortality in a dose-dependent manner. With 2 mg T3/kg, mortality in the BC-line was almost double that in the A-line. 6. These studies indicate that the development of ascites could be linked with thyroid function. Moreover, dietary T3 supplementation could be used to help identify ascites-inducing factors or genetic lines with differential sensitivity for ascites.

Growth of Candida utilis in solid state fermentation

In this work, the growth of the yeast Candida utilis on different solid substrate (wheat bran) and supports (sugarcane bagasse and Amberlite resin) imbibed with a liquid culture medium was studied. Growth was followed by sugars consumption, carbon dioxide production rate (CDPR) and cell count. The results showed the ability of the yeast to grow on the three solid media with fairly good viability and total dextrose consumption in the case of sugarcane bagasse and Amberlite, and partial consumption of wheat bran sugars. After two or three days of culture, a five hundred fold increase in cell population was observed.