Intramolecular coupling as a mechanism for a liquid-liquid phase transition

We study a model for water with a tunable intramolecular interaction Js, using mean-field theory and off-lattice Monte Carlo simulations. For all Js>~0, the model displays a temperature of maximum density. For a finite intramolecular interaction Js>0, our calculations support the presence of a liquid-liquid phase transition with a possible liquid-liquid critical point for water, likely preempted by inevitable freezing. For J=0, the liquid-liquid critical point disappears at T=0.

Canonical formalism for path dependent Lagrangians. Coupling constant expansions

A canonical formalism obtained for path-dependent Lagrangians is applied to Fokker-type Lagrangians. The results are specialized for coupling constant expansions and later on are applied to relativistic systems of particles interacting through symmetric scalar and vector mesodynamics and electrodynamics.

Strong coupling solution to Schrödinger Equation: the mixing of states

In this paper we give some ideas that can be useful to solve Schrödinger equations in the case when the Hamiltonian contains a large term. We obtain an expansion of the solution in reciprocal powers of the large coupling constant. The procedure followed consists in considering that the small part of the Hamiltonian engenders a motion adiabatic to the motion generated by the large part of the same.

Hypertriglyceridemia: a potential side effect of propofol sedation in critical illness.

PURPOSE: Hypertriglyceridemia (hyperTG) is common among intensive care unit (ICU) patients, but knowledge about hyperTG risk factors is scarce. The present study aims to identify risk factors favoring its development in patients requiring prolonged ICU treatment. METHODS: Prospective observational study in the medicosurgical ICU of a university teaching hospital. All consecutive patients staying ≥4 days were enrolled. Potential risk factors were recorded: pathology, energy intake, amount and type of nutritional lipids, intake of propofol, glucose intake, laboratory parameters, and drugs. Triglyceride (TG) levels were assessed three times weekly. Statistics was based on two-way analysis of variance (ANOVA) and linear regression with potential risk factors. RESULTS: Out of 1,301 consecutive admissions, 220 patients were eligible, of whom 99 (45 %) presented hyperTG (triglycerides >2 mmol/L). HyperTG patients were younger, heavier, with more brain injury and multiple trauma. Intake of propofol (mg/kg/h) and lipids' propofol had the highest correlation with plasma TG (r (2) = 0.28 and 0.26, respectively, both p < 0.001). Infection and inflammation were associated with development of hyperTG [C-reactive protein (CRP), r (2) = 0.19, p = 0.004]. No strong association could be found with nutritional lipids or other risk factors. Outcome was similar in normo- and hyperTG patients. CONCLUSIONS: HyperTG is frequent in the ICU but is not associated with adverse outcome. Propofol and accompanying lipid emulsion are the strongest risk factors. Our results suggest that plasma TG should be monitored at least twice weekly in patients on propofol. The clinical consequences of propofol-related hyperTG should be investigated in further studies.

Ab initio theoretical comparative study of magnetic coupling in KNiF3 and K2NiF4s

The origin of magnetic coupling in KNiF3 and K2 NiF4 is studied by means of an ab initio cluster model approach. By a detailed study of the mapping between eigenstates of the exact nonrelativistic and spin model Hamiltonians it is possible to obtain the magnetic coupling constant J and to compare ab initio cluster-model values with those resulting from ab initio periodic Hartree-Fock calculations. This comparison shows that J is strongly determined by two-body interactions; this is a surprising and unexpected result. The importance of the ligands surrounding the basic metal-ligand-metal interacting unit is reexamined by using two different partitions and the constrained space orbital variation method of analysis. This decomposition enables us to show that this effect is basically environmental. Finally, dynamical electronic correlation effects have found to be critical in determining the final value of the magnetic coupling constant.

Local character of magnetic coupling in ionic solids

Magnetic interactions in ionic solids are studied using parameter-free methods designed to provide accurate energy differences associated with quantum states defining the Heisenberg constant J. For a series of ionic solids including KNiF3, K2NiF4, KCuF3, K2CuF4, and high- Tc parent compound La2CuO4, the J experimental value is quantitatively reproduced. This result has fundamental implications because J values have been calculated from a finite cluster model whereas experiments refer to infinite solids. The present study permits us to firmly establish that in these wide-gap insulators, J is determined from strongly local electronic interactions involving two magnetic centers only thus providing an ab initio support to commonly used model Hamiltonians.

Magnetic coupling in the weac ferromagnet CuF2

CuF2 is known to be an antiferromagnetic compound with a weak ferromagnetism due to the anisotropy of its monoclinic unit cell (Dzialoshinsky-Moriya mechanism). We investigate the magnetic ordering of this compound by means of ab initio periodic unrestricted Hartree-Fock calculations and by cluster calculations which employ state-of-the-art configuration interaction expansions and modern density functional theory techniques. The combined use of periodic and cluster models permits us to firmly establish that the antiferromagnetic order arises from the coupling of one-dimensional subunits which themselves exhibit a very small ferromagnetic coupling between Cu neighbor cations. This magnetic order could be anticipated from the close correspondence between CuF2 and rutile crystal structures.

Whole-body vibration training: metabolic cost of synchronous, side-alternating or no vibrations.

Whole-body vibration training improves strength and can increase maximal oxygen consumption ([·V]O(2max)). No study has compared the metabolic demand of synchronous and side-alternating whole-body vibration. We measured [·V]O₂ and heart rate during a typical synchronous or side-alternating whole-body vibration session in 10 young female sedentary participants. The 20-min session consisted of three sets of six 45-s exercises, with 15 s recovery between exercises. Three conditions were randomly tested on separate days: synchronous at 35 Hz and 4 mm amplitude, side-alternating at 26 Hz and 7.5 mm amplitude (peak acceleration matched at 20 g in both vibration conditions), and no vibrations. Mean [·V]O₂ (expressed as %[·V]O(2max)) did not differ between conditions: 29.7 ± 4.2%, 32.4 ± 6.5%, and 28.7 ± 6.7% for synchronous, side-alternating, and no vibrations respectively (P = 0.103). Mean heart rate (% maximal heart rate) was 65.6 ± 7.3%, 69.8 ± 7.9%, and 64.7 ± 5.6% for synchronous, side-alternating, and no vibrations respectively, with the side-alternating vibrations being significantly higher (P = 0.019). When analysing changes over exercise sessions, mean [·V]O₂ was higher for side-alternating (P < 0.001) than for synchronous and no vibrations. In conclusion, side-alternating whole-body vibration elicits higher heart rate responses than synchronous or no vibrations, and could elevate [·V]O₂, provided the session lasts more than 20 min.

Angiotensin II-mediated adaptive and maladaptive remodeling of cardiomyocyte excitation-contraction coupling.

Cardiac hypertrophy is associated with alterations in cardiomyocyte excitation-contraction coupling (ECC) and Ca(2+) handling. Chronic elevation of plasma angiotensin II (Ang II) is a major determinant in the pathogenesis of cardiac hypertrophy and congestive heart failure. However, the molecular mechanisms by which the direct actions of Ang II on cardiomyocytes contribute to ECC remodeling are not precisely known. This question was addressed using cardiac myocytes isolated from transgenic (TG1306/1R [TG]) mice exhibiting cardiac specific overexpression of angiotensinogen, which develop Ang II-mediated cardiac hypertrophy in the absence of hemodynamic overload. Electrophysiological techniques, photolysis of caged Ca(2+) and confocal Ca(2+) imaging were used to examine ECC remodeling at early ( approximately 20 weeks of age) and late ( approximately 60 weeks of age) time points during the development of cardiac dysfunction. In young TG mice, increased cardiac Ang II levels induced a hypertrophic response in cardiomyocyte, which was accompanied by an adaptive change of Ca(2+) signaling, specifically an upregulation of the Na(+)/Ca(2+) exchanger-mediated Ca(2+) transport. In contrast, maladaptation was evident in older TG mice, as suggested by reduced sarcoplasmic reticulum Ca(2+) content resulting from a shift in the ratio of plasmalemmal Ca(2+) removal and sarcoplasmic reticulum Ca(2+) uptake. This was associated with a conserved ECC gain, consistent with a state of hypersensitivity in Ca(2+)-induced Ca(2+) release. Together, our data suggest that chronic elevation of cardiac Ang II levels significantly alters cardiomyocyte ECC in the long term, and thereby contractility, independently of hemodynamic overload and arterial hypertension.

Site-specific coupling between vascular wall thickness and function: an observational MRI study of vessel wall thickening and stiffening in hypertension.

OBJECTIVES: The objective of this study was to evaluate associations between aortic pulse wave velocity (PWV) and aortic and carotid vessel wall thickness (VWT) using cardiovascular magnetic resonance imaging (MRI) in patients with hypertension as compared with healthy adult volunteers. MATERIALS AND METHODS: Local medical ethics approval was obtained and the participants gave informed consent. Fifteen patients with hypertension (5 men and 10 women; mean [SD] age, 49 [14] years) and 15 age- and sex-matched healthy volunteers were prospectively included and compared. All participants underwent MRI examination for measuring aortic and carotid VWT and aortic PWV with well-validated MRI techniques at 1.5- and 3-T MRI systems: PWV was assessed from velocity-encoded MRI and VWT was assessed by using dual-inversion black-blood gradient-echo imaging techniques. Paired t tests were used for testing differences between the volunteers and the patients and Pearson correlation (r) and univariable and multivariable stepwise linear regression analyses were used to test associations between aortic and carotid arterial wall thickness and stiffness. RESULTS: Mean values for aortic PWV and aortic and carotid VWT (indexed for body surface area [BSA]) were all significantly higher in patients with hypertension as compared with the healthy volunteers (ie, aortic PWV, 7.0 ± 1.4 m/s vs 5.7 ± 1.3 m/s; aortic VWT/BSA, 0.12 ± 0.03 mL/m vs 0.10 ± 0.03 mL/m; carotid VWT/BSA, 0.04 ± 0.01 mL/m vs 0.03 ± 0.01 mL/m; all P < 0.01). Aortic PWV was highly correlated with aortic VWT/BSA (r = 0.76 and P = 0.002 in the patients vs r = 0.63 and P = 0.02 in the volunteers), and in the patients, aortic PWV was moderately correlated with carotid VWT/BSA (r = 0.50; P = 0.04). In the volunteers, correlation between aortic PWV and carotid VWT/BSA was not significant (r = 0.40; P = 0.13). In addition, aortic VWT/BSA was significantly correlated with carotid VWT/BSA, in both the patients (r = 0.60; P = 0.005) and volunteers (r = 0.57; P = 0.007). CONCLUSIONS: In the patients with hypertension and the healthy volunteers, the aortic PWV is associated more strongly with aortic wall thickness than with carotid wall thickness, reflecting site-specific coupling between vascular wall thickness and function.

Can dopamine prevent the renal side effects of indomethacin? A prospective randomized clinical study.

BACKGROUND: Indomethacin therapy for closure of a patent ductus arteriosus in preterm neonates is responsible for transient renal insufficiency. Dopamine theoretically reduces the renal side effects of indomethacin therapy. PATIENTS: 33 neonates with a mean gestational age of 28.5 weeks who received indomethacin for treatment of a symptomatic PDA were included in a prospective randomized controlled clinical study. METHOD: 15 patients were treated with indomethacin alone (control group), 18 patients with indomethacin and dopamine (study group). Indomethacin was given in a dose of 0.2 mg/kg/dose intravenously, all patients received three doses with intervall of 12 hours. The dose of dopamine was in all patients 4 micrograms/kg per minute commencing 2 hours prior to the first dose of indomethacin and continuing for 12 hours after the third dose. RESULTS: Indomethacin induced a significant increase in serum creatinin (76.3 mumol/l vs 99.7 mumol/l for the control group, and 70.7 mumol/l vs 93.0 mumol/l for the study group), and weight (1259 g vs 1316 g for the control group, and 1187 g vs 1221 g for the study group). The increase systolic blood pressure (61 mmHg vs 65.7 mmHg) in the study group was significant (p < 0.05) but remained unchanged in the control group. The changes between the study group and the control group were not significant either in serum creatinin, fractional excretion of sodium, or weight gain. The failure rate of ductal closure was not different between the two groups. CONCLUSION: The additional use of dopamine does not reduce the renal side effects of indomethacin.

Five years of sleep apnea treatment with a mandibular advancement device. Side effects and technical complications

Objective: To determine the variation in prevalence of temporomandibular disorders (TMD), other side effects, and technical complications during 5 years of sleep apnea treatment with a mandibular advancement device. Materials and Methods: Forty patients diagnosed with obstructive sleep apnea received an adjustable appliance at 70% of the maximum protrusion. The protrusion was then progressively increased. TMD (diagnosed according to the Research Diagnostic Criteria for TMD), overjet, overbite, occlusal contacts, subjective side effects, and technical complications were recorded before and a mean of 14, 21, and 58 months after treatment and analyzed by the Wilcoxon test (P Less-than .05). Results: Fifteen patients still used the oral appliance at the 5-year follow-up, and no significant variation in TMD prevalence was observed. Subjective side effects were common, and a significant reduction was found in overjet, overbite, and in the number of occlusal contacts. Furthermore, the patients made a mean of 2.5 unscheduled dental visits per year and a mean of 0.8 appliance repairs/relines per year by a dental technician. The most frequent unscheduled visits were needed during the first year and were a result of acrylic breakage on the lateral telescopic attachment, poor retention, and other adjustments to improve comfort. Conclusions: Five-year oral appliance treatment does not affect TMD prevalence but is associated with permanent occlusal changes in most sleep apnea patients during the first 2 years. Patients seek several unscheduled visits, mainly because of technical complications.

Role of glutamate in neuron-glia metabolic coupling.

The coupling between synaptic activity and glucose utilization (neurometabolic coupling) is a central physiologic principle of brain function that has provided the basis for 2-deoxyglucose-based functional imaging with positron emission tomography. Approximately 10 y ago we provided experimental evidence that indicated a central role of glutamate signaling on astrocytes in neurometabolic coupling. The basic mechanism in neurometabolic coupling is the glutamate-stimulated aerobic glycolysis in astrocytes, such that the sodium-coupled reuptake of glutamate by astrocytes and the ensuing activation of the Na(+)-K(+) ATPase triggers glucose uptake and its glycolytic processing, which results in the release of lactate from astrocytes. Lactate can then contribute to the activity-dependent fueling of the neuronal energy demands associated with synaptic transmission. Analyses of this coupling have been extended in vivo and have defined the methods of coupling for inhibitory neurotransmission as well as its spatial extent in relation to the propagation of metabolic signals within the astrocytic syncytium. On the basis of a large body of experimental evidence, we proposed an operational model, "the astrocyte-neuron lactate shuttle." A series of results obtained by independent laboratories have provided further support for this model. This body of evidence provides a molecular and cellular basis for interpreting data that are obtained with functional brain imaging studies.