924 research outputs found
Renormalization Group Study of the soliton mass on the (lambda Phi^4)_{1+1} lattice model
We compute, on the model on the lattice, the soliton
mass by means of two very different numerical methods. First, we make use of a
``creation operator'' formalism, measuring the decay of a certain correlation
function. On the other hand we measure the shift of the vacuum energy between
the symmetric and the antiperiodic systems. The obtained results are fully
compatible.
We compute the continuum limit of the mass from the perturbative
Renormalization Group equations. Special attention is paid to ensure that we
are working on the scaling region, where physical quantities remain unchanged
along any Renormalization Group Trajectory. We compare the continuum value of
the soliton mass with its perturbative value up to one loop calculation. Both
quantities show a quite satisfactory agreement. The first is slightly bigger
than the perturbative one; this may be due to the contributions of higher order
corrections.Comment: 19 pages, preprint DFTUZ/93/0
Nonequilibrium Electron Interactions in Metal Films
Ultrafast relaxation dynamics of an athermal electron distribution is
investigated in silver films using a femtosecond pump-probe technique with 18
fs pulses in off-resonant conditions. The results yield evidence for an
increase with time of the electron-gas energy loss rate to the lattice and of
the free electron damping during the early stages of the electron-gas
thermalization. These effects are attributed to transient alterations of the
electron average scattering processes due to the athermal nature of the
electron gas, in agreement with numerical simulations
Effectiveness and cost-effectiveness of a nurse-delivered intervention to improve adherence to treatment for HIV : a pragmatic, multicentre, open-label, randomised clinical trial
This trial was funded from public money by the Netherlands Organisation for Health Research and Development (ZonMW; grant number 171002208). Aardex provided support on the development of the study website. We thank all the HIV nurses and physicians from the seven HIV clinics involved in the AIMS study for their input and collaboration (Academic Medical Centre, Slotervaart hospital, and St. Lucas-Andreas hospital, all in Amsterdam; the Leiden University Medical Centre, Leiden; HAGA hospital, The Hague; Erasmus Medical Centre, Rotterdam; and Isala clinic, Zwolle), the study participants, and the Stichting HIV Monitoring (SHM) for their support in accessing the SHM database for identifying patient inclusion criteria and developing the Markov model. Finally, we thank and remember Herman Schaalma (deceased) for his contribution to the study design and grant application.Peer reviewedPostprin
Ultrafast dynamics of coherent optical phonons and nonequilibrium electrons in transition metals
The femtosecond optical pump-probe technique was used to study dynamics of
photoexcited electrons and coherent optical phonons in transition metals Zn and
Cd as a function of temperature and excitation level. The optical response in
time domain is well fitted by linear combination of a damped harmonic
oscillation because of excitation of coherent phonon and a
subpicosecond transient response due to electron-phonon thermalization. The
electron-phonon thermalization time monotonically increases with temperature,
consistent with the thermomodulation scenario, where at high temperatures the
system can be well explained by the two-temperature model, while below
50 K the nonthermal electron model needs to be applied. As the
lattice temperature increases, the damping of the coherent phonon
increases, while the amplitudes of both fast electronic response and the
coherent phonon decrease. The temperature dependence of the damping of
the phonon indicates that population decay of the coherent optical
phonon due to anharmonic phonon-phonon coupling dominates the decay process. We
present a model that accounts for the observed temperature dependence of the
amplitude assuming the photoinduced absorption mechanism, where the signal
amplitude is proportional to the photoinduced change in the quasiparticle
density. The result that the amplitude of the phonon follows the
temperature dependence of the amplitude of the fast electronic transient
indicates that under the resonant condition both electronic and phononic
responses are proportional to the change in the dielectric function.Comment: 10 pages, 9 figures, to appear in Physical Review
Relaxation Dynamics of Photoinduced Changes in the Superfluid Weight of High-Tc Superconductors
In the transient state of d-wave superconductors, we investigate the temporal
variation of photoinduced changes in the superfluid weight. We derive the
formula that relates the nonlinear response function to the nonequilibrium
distribution function. The latter qunatity is obtained by solving the kinetic
equation with the electron-electron and the electron-phonon interaction
included. By numerical calculations, a nonexponential decay is found at low
temperatures in contrast to the usual exponential decay at high temperatures.
The nonexponential decay originates from the nonmonotonous temporal variation
of the nonequilibrium distribution function at low energies. The main physical
process that causes this behavior is not the recombination of quasiparticles as
previous phenomenological studies suggested, but the absorption of phonons.Comment: 18 pages, 12 figures; to be published in J. Phys. Soc. Jpn. Vol. 80,
No.
Clinical Applicability of Transient Elastography for Estimating Liver Stiffness in Patients with Type 2 Diabetes Mellitus
Background: Type 2 diabetes mellitus (T2DM) is a risk factor for the development of non-alcoholic fatty liver disease, which can lead to liver fibrosis and ultimately to cirrhosis. Transient elastography (TE), by using the FibroScan, and is a non-invasive ultrasonography method to measure liver elasticity. TE has been related with the degree of liver fibrosis. Objective: To investigate the applicability of TE in daily clinical practice among T2DM patients. Method: In a non-academic teaching hospital, T2DM patients without a history of liver disease the degree of liver stiffness was measured using TE. Successful measurements were defined as 10 validated measurements per patient and an interquartile range (IQR) to median ratio of ≤30%. Results: In 90 of 126 patients (71%) valid measurements were be obtained. Among the patients with invalid measurements, 33 had < 10 valid measurements and 3 had a IQR to median ratio of <30%. The percentage of invalid measurements was 12% in patients with a BMI <30 kg/m2 and 39% in patients with a BMI ≥30 kg/m2. Among the 90 patients with valid liver stiffness measurements, the median liver stiffness was 6.7 [4.6-8.5] kPa with a IQR of measurements of 1.1 [0.6-1.8] kPa and IQR to median ratio of 17 (13-23)%. Conclusion: The success rate of TE measurements using the FibroScan in patients with T2DM was 71%, with a lower success rate in patients with a BMI ≥ 30 kg/m2. This diagnostic modality needs further investigation being introduced as a marker of fibrosis in daily diabetes practice
Sex Hormone Binding Globulin Deficiency Due to a Homozygous Missense Mutation
Context: SHBG is known as the major sex steroid binding protein in plasma, and it regulates the bioavailability of both T and estradiol levels required for effects on target tissues. We identified a man with an undetectable SHBG concentration in combination with low total T. He presented with a 7-year history of muscle weakness, fatigue, and a low libido. Objectives: To determine the cause of the SHBG deficiency, we employed both genetic analysis of the SHBG gene and transgene SHBG expression. Results: Genetic analysis identified a novel homozygous missense mutation that was predicted to be deleterious for protein function. Transgene expression showed that the mutation resulted in a block in SHBG secretion accompanied by increased expression of the endoplasmic reticulum molecular chaperone HSPA5. The mutation results in accumulation of the mutant SHBG within the cell and failure to secrete the mutant protein. Screening of family members identified one sister who was also deficient for SHBG. Conclusions: We have identified a family with a missense mutation within the SHBG gene, which results in a complete deficiency of plasma SHBG in the homozygous state. Although total T level was low in the male patient, it did not interfere with normal gonadal development and spermatogenesis, suggesting a limited role of SHBG in sexual maturation and male physiology
Photochromism in Ruddlesden-Popper copper-based perovskites:A light-induced change of coordination number at the surface
Ruddlesden-Popper organic-inorganic hybrid copper-based perovskites have been studied for decades owing to a variety of interesting properties, such as thermochromism and piezochromism, and the mechanisms behind these phenomena have been explained. Another possible property of these materials that has seldomly been investigated is photochromism. In this work, the photochromic properties of bis(phenethylammonium) tetrachlorocuprate (also known as phenethylammonium copper chloride) are reported for the first time. This material has attracted scientific interest owing to the fact that it shows both ferroelectric and ferromagnetic behavior. This work highlights the difference in stability between two Ruddlesden-Popper copper-based perovskites - with phenethylammonium (PEA) or methylammonium (MA) as the cations - during external stimuli. Various techniques, such as Raman and X-ray photoelectron spectroscopy, and grazing-incidence wide-angle X-ray scattering, combined with optical studies, were used to investigate the underlying photochemical processes at a molecular level. It is found that for the PEA compound, ultraviolet illumination causes a color change from yellow to brown. This is the result of two independent events, namely a Cu2+ reduction reaction and a transition from an octahedral copper-chloride structure to square-planar CuCl42-. After illumination, the material (brown color) is unstable in air, which is evident from a color change back to yellow. Interestingly, the similar compound bis(methylammonium) tetrachlorocuprate does not display photochromic behavior, which is attributed to the different nature of the two organic cations
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