156 research outputs found
Bulk and shear relaxation in glasses and highly viscous liquids
The ratio between the couplings of a relaxational process to compression and
shear, respectively, is calculated in the Eshelby picture of structural
rearrangements within a surrounding elastic matrix, assuming a constant density
of stable structures in distortion space. The result is compared to
experimental data for the low-temperature tunneling states in glasses and to
Prigogine-Defay data at the glass transition from the literature.Comment: 6 pages, 2 figures, 53 references; version after understanding the
Prigogine-Defay ratio at the glass transition in the accompanying paper
arXiv:1203.3555 [cond-mat.dis-nn
Molecular gyroscopes and biological effects of weak ELF magnetic fields
Extremely-low-frequency magnetic fields are known to affect biological
systems. In many cases, biological effects display `windows' in biologically
effective parameters of the magnetic fields: most dramatic is the fact that
relatively intense magnetic fields sometimes do not cause appreciable effect,
while smaller fields of the order of 10--100 T do. Linear resonant
physical processes do not explain frequency windows in this case. Amplitude
window phenomena suggest a nonlinear physical mechanism. Such a nonlinear
mechanism has been proposed recently to explain those `windows'. It considers
quantum-interference effects on protein-bound substrate ions. Magnetic fields
cause an interference of ion quantum states and change the probability of
ion-protein dissociation. This ion-interference mechanism predicts specific
magnetic-field frequency and amplitude windows within which biological effects
occur. It agrees with a lot of experiments. However, according to the
mechanism, the lifetime of ion quantum states within a protein
cavity should be of unrealistic value, more than 0.01 s for frequency band
10--100 Hz. In this paper, a biophysical mechanism has been proposed that (i)
retains the attractive features of the ion interference mechanism and (ii) uses
the principles of gyroscopic motion and removes the necessity to postulate
large lifetimes. The mechanism considers dynamics of the density matrix of the
molecular groups, which are attached to the walls of protein cavities by two
covalent bonds, i.e., molecular gyroscopes. Numerical computations have shown
almost free rotations of the molecular gyros. The relaxation time due to van
der Waals forces was about 0.01 s for the cavity size of 28 angstr\"{o}ms.Comment: 10 pages, 7 figure
Temperature dependence of bulk viscosity in water using acoustic spectroscopy
Despite its fundamental role in the dynamics of compressible fluids, bulk
viscosity has received little experimental attention and there remains a
paucity of measured data. Acoustic spectroscopy provides a robust and accurate
approach to measuring this parameter. Working from the Navier-Stokes model of a
compressible fluid one can show that the bulk viscosity makes a significant and
measurable contribution to the frequency-squared acoustic attenuation. Here we
employ this methodology to determine the bulk viscosity of Millipore water over
a temperature range of 7 to 50 degrees Celsius. The measured attenuation
spectra are consistent with the theoretical predictions, while the bulk
viscosity of water is found to be approximately three times larger than its
shear counterpart, reinforcing its significance in acoustic propagation.
Moreover, our results demonstrate that this technique can be readily and
generally applied to fluids to accurately determine their temperature dependent
bulk viscosities.Comment: 7 pages, 4 figures. Proceedings of the Anglo-French Physical
Acoustics Conference, January 201
Inhibition of G Protein-Activated Inwardly Rectifying K+ Channels by Different Classes of Antidepressants
Various antidepressants are commonly used for the treatment of depression and several other neuropsychiatric disorders. In addition to their primary effects on serotonergic or noradrenergic neurotransmitter systems, antidepressants have been shown to interact with several receptors and ion channels. However, the molecular mechanisms that underlie the effects of antidepressants have not yet been sufficiently clarified. G protein-activated inwardly rectifying K+ (GIRK, Kir3) channels play an important role in regulating neuronal excitability and heart rate, and GIRK channel modulation has been suggested to have therapeutic potential for several neuropsychiatric disorders and cardiac arrhythmias. In the present study, we investigated the effects of various classes of antidepressants on GIRK channels using the Xenopus oocyte expression assay. In oocytes injected with mRNA for GIRK1/GIRK2 or GIRK1/GIRK4 subunits, extracellular application of sertraline, duloxetine, and amoxapine effectively reduced GIRK currents, whereas nefazodone, venlafaxine, mianserin, and mirtazapine weakly inhibited GIRK currents even at toxic levels. The inhibitory effects were concentration-dependent, with various degrees of potency and effectiveness. Furthermore, the effects of sertraline were voltage-independent and time-independent during each voltage pulse, whereas the effects of duloxetine were voltage-dependent with weaker inhibition with negative membrane potentials and time-dependent with a gradual decrease in each voltage pulse. However, Kir2.1 channels were insensitive to all of the drugs. Moreover, the GIRK currents induced by ethanol were inhibited by sertraline but not by intracellularly applied sertraline. The present results suggest that GIRK channel inhibition may reveal a novel characteristic of the commonly used antidepressants, particularly sertraline, and contributes to some of the therapeutic effects and adverse effects
Comparative outcome analysis of home-initiated non-medical interventions among toddlers with orally ingested substances
Circumstances and factors associated with accidental deaths among children, adolescents and young adults in Cuiaba, Brazil
A retrospective analysis of glycol and toxic alcohol ingestion: utility of anion and osmolal gaps
<p>Abstract</p> <p>Background</p> <p>Patients ingesting ethylene glycol, isopropanol, methanol, and propylene glycol ('toxic alcohols') often present with non-specific signs and symptoms. Definitive diagnosis of toxic alcohols has traditionally been by gas chromatography (GC), a technique not commonly performed on-site in hospital clinical laboratories. The objectives of this retrospective study were: 1) to assess the diagnostic accuracy of the osmolal gap in screening for toxic alcohol ingestion and 2) to determine the common reasons other than toxic alcohol ingestion for elevated osmolal gaps.</p> <p>Methods</p> <p>Electronic medical records from an academic tertiary care medical center were searched to identify all patients in the time period from January 1, 1996 to September 1, 2010 who had serum/plasma ethanol, glucose, sodium, blood urea nitrogen, and osmolality measured simultaneously, and also all patients who had GC analysis for toxic alcohols. Detailed chart review was performed on all patients with osmolal gap of 9 or greater.</p> <p>Results</p> <p>In the study period, 20,669 patients had determination of serum/plasma ethanol and osmolal gap upon presentation to the hospitals. There were 341 patients with an osmolal gap greater than 14 (including correction for estimated contribution of ethanol) on initial presentation to the medical center. Seventy-seven patients tested positive by GC for one or more toxic alcohols; all had elevated anion gap or osmolal gap or both. Other than toxic alcohols, the most common causes for an elevated osmolal gap were recent heavy ethanol consumption with suspected alcoholic ketoacidosis, renal failure, shock, and recent administration of mannitol. Only 9 patients with osmolal gap greater than 50 and no patients with osmolal gap greater than 100 were found to be negative for toxic alcohols.</p> <p>Conclusions</p> <p>Our study concurs with other investigations that show that osmolal gap can be a useful diagnostic test in conjunction with clinical history and physical examination.</p
Unified treatment algorithm for the management of crotaline snakebite in the United States: results of an evidence-informed consensus workshop
<p>Abstract</p> <p>Background</p> <p>Envenomation by crotaline snakes (rattlesnake, cottonmouth, copperhead) is a complex, potentially lethal condition affecting thousands of people in the United States each year. Treatment of crotaline envenomation is not standardized, and significant variation in practice exists.</p> <p>Methods</p> <p>A geographically diverse panel of experts was convened for the purpose of deriving an evidence-informed unified treatment algorithm. Research staff analyzed the extant medical literature and performed targeted analyses of existing databases to inform specific clinical decisions. A trained external facilitator used modified Delphi and structured consensus methodology to achieve consensus on the final treatment algorithm.</p> <p>Results</p> <p>A unified treatment algorithm was produced and endorsed by all nine expert panel members. This algorithm provides guidance about clinical and laboratory observations, indications for and dosing of antivenom, adjunctive therapies, post-stabilization care, and management of complications from envenomation and therapy.</p> <p>Conclusions</p> <p>Clinical manifestations and ideal treatment of crotaline snakebite differ greatly, and can result in severe complications. Using a modified Delphi method, we provide evidence-informed treatment guidelines in an attempt to reduce variation in care and possibly improve clinical outcomes.</p
DEPOLARIZED RAYLEIGH SCATTERINGDEPOLARIZED RAYLEIGH AND RAMAN SCATTERING : MECHANISM OF ORIENTATIONAL MOTION IN LIQUIDS
En se servant Ă la fois des largeurs de raie Rayleigh et Raman, on a entrepris une Ă©tude systĂ©matique de 15 liquides, pour dĂ©terminer le mĂ©canisme du processus de rĂ©orientation. On a trouvĂ© qu'on peut classer les liquides selon que la rĂ©orientation est dĂ©terminĂ©e par la dynamique de la structure ou les mouvements dus aux collisions. Pour les liquides «limitĂ©s par les collisions» (par exemple CCl4, CS2) on a obtenu le temps entre collisions ÏBC en appliquant l'Ă©quation d'Hubbard aux donnĂ©es de la diffusion de la lumiĂšre. Les valeurs de ÏBC en fonction de la tempĂ©rature sont en bon accord avec le modĂšle cellulaire de la structure des liquides. On suggĂšre que les liquides liĂ©s par ponts hydrogĂšne ou par empĂȘchement stĂ©rique (par exemple l'eau ou la nitrobenzĂšne) possĂšdent un processus de rĂ©orientation qui est reliĂ© de prĂšs au temps de relaxation de structure d'un rĂ©seau liquide.Using both Rayleigh and Raman linewidths a systematic study of 15 liquids was undertaken to determine the mechanism of the reorientation process. It was found that liquids could be classified according to whether reorientation is determined by structural dynamics or collisional motions. For «collision limited » liquids (e. g. CCl4, CS2) the time between collisions, ÏBC was obtained by applying the Hubbard equation to the light scattering data. The values of ÏBC vs temperature agree well with the cell model of liquid structure. It is suggested that hydrogen bonded and sterically hindered liquids (e. g. water, nitrobenzene) have areorientation process which is closely related to the structural relaxation time of the liquid lattice
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