7,702 research outputs found
Conformational Mechanics of Polymer Adsorption Transitions at Attractive Substrates
Conformational phases of a semiflexible off-lattice homopolymer model near an
attractive substrate are investigated by means of multicanonical computer
simulations. In our polymer-substrate model, nonbonded pairs of monomers as
well as monomers and the substrate interact via attractive van der Waals
forces. To characterize conformational phases of this hybrid system, we analyze
thermal fluctuations of energetic and structural quantities, as well as
adequate docking parameters. Introducing a solvent parameter related to the
strength of the surface attraction, we construct and discuss the
solubility-temperature phase diagram. Apart from the main phases of adsorbed
and desorbed conformations, we identify several other phase transitions such as
the freezing transition between energy-dominated crystalline low-temperature
structures and globular entropy-dominated conformations.Comment: 13 pages, 15 figure
Microcanonical entropy inflection points: Key to systematic understanding of transitions in finite systems
We introduce a systematic classification method for the analogs of phase
transitions in finite systems. This completely general analysis, which is
applicable to any physical system and extends towards the thermodynamic limit,
is based on the microcanonical entropy and its energetic derivative, the
inverse caloric temperature. Inflection points of this quantity signal
cooperative activity and thus serve as distinct indicators of transitions. We
demonstrate the power of this method through application to the long-standing
problem of liquid-solid transitions in elastic, flexible homopolymers.Comment: 4 pages, 3 figure
A simple quantum cosmology
A simple and surprisingly realistic model of the origin of the universe can
be developed using the Friedmann equation from general relativity, elementary
quantum mechanics, and the experimental values of h, c, G and the proton mass.
The model assumes there are N space dimensions (with N > 6) and the potential
constraining the radius r of the invisible N -3 compact dimensions varies as
r^4. In this model, the universe has zero total energy and is created from
nothing. There is no initial singularity. If space-time is eleven dimensional,
as required by M theory, the scalar field corresponding to the size of the
compact dimensions inflates the universe by about 26 orders of magnitude (60
e-folds). If the Hubble constant is 65 km/sec Mpc, the energy density of the
scalar field after inflation results in Omega-sub-Lambda = 0.68, in agreement
with recent astrophysical observations.Comment: To be published in General Relativity and Gravitation, August 200
Genetic analysis of aMicroseris douglasii (Asteraceae) population polymorphic for an alien chloroplast type
Measurement of the magnetic octupole susceptibility of PrV2Al20
In the electromagnetic multipole expansion, magnetic octupoles are the
subsequent order of magnetic multipoles allowed in centrosymmetric systems,
following the more commonly observed magnetic dipoles. As order parameters in
condensed matter systems, magnetic octupoles have been experimentally elusive.
In particular, the lack of simple external fields that directly couple to them
makes their experimental detection challenging. Here, we demonstrate a
methodology for probing the magnetic octupole susceptibility using a product of
magnetic field and shear strain to couple to the
octupolar fluctuations, while using an adiabatic elastocaloric effect to probe
the response to this composite effective field. We observe a Curie-Weiss
behavior in the obtained octupolar susceptibility of \ce{PrV2Al20} up to
temperatures approximately forty times the putative octupole ordering
temperature. Our results demonstrate the presence of magnetic octupole
fluctuations in the particular material system, and more broadly highlight how
anisotropic strain can be combined with magnetic fields to formulate a
versatile probe to observe otherwise elusive emergent `hidden' electronic
orders.Comment: 7 pages, 3 figure
Low absorption InP/InGaAs-MQW phase shifters for optical switching
InP/InGaAs-MQW phase shifters with low absorption loss and low electroabsorption loss have been realized. Phase shift efficiency for TE-polarized light at lambda =1.55 mu m was 6.8 degrees V/sup -1/ mm/sup -1/ with negligible absorption loss and at lambda =1.51 mu m the efficiency was 8.9 degrees V/sup -1/ mm/sup -1/ with 5 dB/cm absorption los
Electronic in-plane symmetry breaking at field-tuned quantum criticality in CeRhIn5
Electronic nematics are exotic states of matter where electronic interactions
break a rotational symmetry of the underlying lattice, in analogy to the
directional alignment without translational order in nematic liquid crystals.
Intriguingly such phases appear in the copper- and iron-based superconductors,
and their role in establishing high-temperature superconductivity remains an
open question. Nematicity may take an active part, cooperating or competing
with superconductivity, or may appear accidentally in such systems. Here we
present experimental evidence for a phase of nematic character in the heavy
fermion superconductor CeRhIn5. We observe a field-induced breaking of the
electronic tetragonal symmetry of in the vicinity of an antiferromagnetic (AFM)
quantum phase transition at Hc~50T. This phase appears in out-of-plane fields
of H*~28T and is characterized by substantial in-plane resistivity anisotropy.
The anisotropy can be aligned by a small in-plane field component, with no
apparent connection to the underlying crystal structure. Furthermore no
anomalies are observed in the magnetic torque, suggesting the absence of
metamagnetic transitions in this field range. These observations are indicative
of an electronic nematic character of the high field state in CeRhIn5. The
appearance of nematic behavior in a phenotypical heavy fermion superconductor
highlights the interrelation of nematicity and unconventional
superconductivity, suggesting nematicity to be a commonality in such materials
Recursive Graphical Construction for Feynman Diagrams of Quantum Electrodynamics
We present a method for a recursive graphical construction of Feynman
diagrams with their correct multiplicities in quantum electrodynamics. The
method is first applied to find all diagrams contributing to the vacuum energy
from which all n-point functions are derived by functional differentiation with
respect to electron and photon propagators, and to the interaction. Basis for
our construction is a functional differential equation obeyed by the vacuum
energy when considered as a functional of the free propagators and the
interaction. Our method does not employ external sources in contrast to
traditional approaches.Comment: Author Information under
http://www.physik.fu-berlin.de/~kleinert/institution.html Latest update of
paper also at http://www.physik.fu-berlin.de/~kleinert/29
Detailing the effects of polypharmacy in psychiatry: longitudinal study of 320 patients hospitalized for depression or schizophrenia
Current treatment standards in psychiatry are oriented towards polypharmacy, that is, patients receive combinations of several antidepressants, antipsychotics, mood stabilizers, anxiolytics, hypnotics, antihistamines, and anticholinergics, along with other somatic treatments. In tandem with the beneficial effects of psychopharmacological drug treatment, patients experience significant adverse reactions which appear to have become more frequent and more severe with the rise of ubiquitous polypharmacy. In this study, we aimed to assess today's acute inpatient treatment of depressive and schizophrenic disorders with focus on therapeutic strategies, medications, adverse side effects, time course of recovery, and efficacy of treatments. Of particular interest was the weighing of the benefits and drawbacks of polypharmacy regimens. We recruited a total of 320 patients hospitalized at three residential mental health treatment centers with a diagnosis of either schizophrenic (ICD-10: "F2x.x"; n = 94; "F2 patients") or depressive disorders (ICD-10: "F3x.x"; n = 226; "F3 patients"). The study protocol included (1) assessment of previous history by means of the SADS Syndrome Check List SSCL-16 (lifetime version); (2) repeated measurements over 5 weeks assessing the time course of improvement by the Hamilton Depression Scale HAM-D and the Positive and Negative Syndrome Scale PANSS, along with medications and adverse side effects through the Medication and Side Effects Inventory MEDIS; and (3) the collection of blood samples from which DNA and serum were extracted. Polypharmacy was by far the most common treatment regimen (85%) in this study. On average, patients received 4.50 ± 2.68 medications, consisting of 3.30 ± 1.84 psychotropic drugs, plus 0.79 ± 1.13 medications that alleviate adverse side effects, plus 0.41 ± 0.89 other somatic medications. The treating psychiatrists appeared to be the main determining factor in this context, while «previous history» and «severity at baseline» played a minor role, if at all. Adverse drug reactions were found to be an inherent component of polypharmacy and tended to have a 2-3 times higher incidence compared to monotherapy. Severe adverse reactions could not be attributed to a particular drug or drug combination. Rather, the empirical data suggested that severe side effects can be triggered by virtually all combinations of drugs, provided patients have a respective vulnerability. In terms of efficacy, there were no advantages of polypharmacy over monotherapy. The results of this study underlined the fact that polypharmacy regimens are not equally suited for every patient. Specifically, such regimens appeared to have a negative impact on treatment outcome and to obfuscate the "natural" time course of recovery through a multitude of interfering factors. Evidence clearly speaks against starting just every therapeutic intervention in psychiatry with a combination of psychopharmaceuticals. We think that it is time for psychiatry to reconsider its treatment strategies, which are far too one-sidedly fixated on psychopharmacology and pay far too little attention to alternative approaches, especially in mild cases where psychotherapy without concurrent medication should still be an option. Also, regular exercises and sports can definitely be an effective therapeutic means in a considerable number of cases. General practitioners (GPs) are particularly in demand here
- …