81 research outputs found
Quantum chaos in nanoelectromechanical systems
We present a theoretical study of the electron-phonon coupling in suspended
nanoelectromechanical systems (NEMS) and investigate the resulting quantum
chaotic behavior. The phonons are associated with the vibrational modes of a
suspended rectangular dielectric plate, with free or clamped boundary
conditions, whereas the electrons are confined to a large quantum dot (QD) on
the plate's surface. The deformation potential and piezoelectric interactions
are considered. By performing standard energy-level statistics we demonstrate
that the spectral fluctuations exhibit the same distributions as those of the
Gaussian Orthogonal Ensemble (GOE) or the Gaussian Unitary Ensemble (GUE),
therefore evidencing the emergence of quantum chaos. That is verified for a
large range of material and geometry parameters. In particular, the GUE
statistics occurs only in the case of a circular QD. It represents an anomalous
phenomenon, previously reported for just a small number of systems, since the
problem is time-reversal invariant. The obtained results are explained through
a detailed analysis of the Hamiltonian matrix structure.Comment: 14 pages, two column
Resonant Production of Scalar Diquarks at the Next Generation Electron-Positron Colliders
We investigate the potential of TESLA and JLC/NLC electron-positron linear
collider designs to observe diquarks produced resonantly in processes involving
hard photons.Comment: 14 pages, 8 figures, coded in RevTEX, uses epsfi
Dispersion force for materials relevant for micro and nanodevices fabrication
The dispersion (van der Waals and Casimir) force between two semi-spaces are
calculated using the Lifshitz theory for different materials relevant for micro
and nanodevices fabrication, namely, gold, silicon, gallium arsenide, diamond
and two types of diamond-like carbon (DLC), silicon carbide, silicon nitride
and silicon dioxide. The calculations were performed using recent experimental
optical data available in the literature, usually ranging from the far infrared
up to the extreme ultraviolet bands of the electromagnetic spectrum. The
results are presented in the form of a correction factor to the Casimir force
predicted between perfect conductors, for the separation between the
semi-spaces varying from 1 nanometre up to 1 micrometre. The relative
importance of the contributions to the dispersion force of the optical
properties in different spectral ranges is analyzed. The role of the
temperature for semiconductors and insulators is also addressed. The results
are meant to be useful for the estimation of the impact of the Casimir and van
der Waals forces on the operational parameters of micro and nanodevices
Static quantities of the W boson in the SU_L(3) X U_X(1) model with right-handed neutrinos
The static electromagnetic properties of the boson, and
, are calculated in the SU_L(3)} \times U_X(1) model with
right-handed neutrinos. The new contributions from this model arise from the
gauge and scalar sectors. In the gauge sector there is a new contribution from
a complex neutral gauge boson and a singly-charged gauge boson .
The mass of these gauge bosons, called bileptons, is expected to be in the
range of a few hundreds of GeV according to the current bounds from
experimental data. If the bilepton masses are of the order of 200 GeV, the size
of their contribution is similar to that obtained in other weakly coupled
theories. However the contributions to both and are
negligible for very heavy or degenerate bileptons. As for the scalar sector, an
scenario is examined in which the contribution to the form factors is
identical to that of a two-Higgs-doublet model. It is found that this sector
would not give large corrections to and .Comment: New material included. Final version to apppear in Physical Review
Two-body decays in the minimal 331 model
The two-body decays of the extra neutral boson Z_2 predicted by the minimal
331 model are analyzed. At the three-level it can decay into standard model
particles as well as exotic quarks and the new gauge bosons predicted by the
model. The decays into a lepton pair are strongly suppressed, with and . In the bosonic
sector, Z_2 would decay mainly into a pair of bilepton gauge bosons, with a
branching ratio below the 0.1 level. The Z_2 boson has thus a leptophobic and
bileptophobic nature and it would decay dominantly into quark pairs. The
anomaly-induced decays and , which occurs
at the one-loop level are studied. It is found that and at most. As for the and decays, with H a relatively light Higgs boson, they
are induced via Z'-Z mixing. It is obtained that
and . We also examine the flavor changing neutral
current decays and , which may have branching
fractions as large as and , respectively, and thus may be of
phenomenological interest.Comment: 14 pages, 3 figures, submitted to Physical Review
Features and frequency of use of electronic health records in primary care across 20 countries:a cross-sectional study
Objectives: Variation exists in the capabilities of electronic healthcare records (EHRs) systems and the frequency of their use by primary care physicians (PCPs) from different settings. We aimed to examine the factors associated with everyday EHRs use by PCPs, characterise the EHRs features available to PCPs, and to identify the impact of practice settings on feature availability. Study design: Cross-sectional study. Methods: PCPs from 20 countries completed cross-sectional online survey between June and September 2020. Responses which reported frequency of EHRs use were retained. Associations between everyday EHRs use and PCP and practice factors (country, urbanicity, and digital maturity) were explored using multivariable logistic regression analyses. The effect of practice factors on the variation in availability of ten EHRs features was estimated using Cramer's V. Results: Responses from 1520 out of 1605 PCPs surveyed (94·7%) were retained. Everyday EHRs use was reported by 91·2% of PCPs. Everyday EHRs use was associated with PCPs working >28 h per week, having more years of experience using EHRs, country of employment, and higher digital maturity. EHRs features concerning entering, and retrieving data were available to most PCPs. Few PCPs reported having access to tools for ‘interactive patient education’ (37·3%) or ‘home monitoring and self-testing of chronic conditions’ (34·3%). Country of practice was associated with availability of all EHRs features (Cramer's V range: 0·2–0·6), particularly with availability of tools enabling patient EHRs access (Cramer's V: 0·6, P < 0.0001). Greater feature availability of EHRs features was observed with greater digital maturity. Conclusions: EHRs features intended for patient use were uncommon across countries and levels of digital maturity. Systems-level research is necessary to identify the country-specific barriers impeding the implementation of EHRs features in primary care, particularly of EHRs features enabling patient interaction with EHRs, to develop strategies to improve systems-wide EHRs use.</p
Poor glycaemic control is associated with reduced exercise performance and oxygen economy during cardio-pulmonary exercise testing in people with type 1 diabetes
BackgroundTo explore the impact of glycaemic control (HbA1c) on functional capacity during cardio-pulmonary exercise testing in people with type 1 diabetes.MethodsSixty-four individuals with type 1 diabetes (age: 34 ± 8 years; 13 females, HbA1c: 7.8 ± 1% (62 ± 13 mmol/mol), duration of diabetes: 17 ± 9 years) performed a cardio-pulmonary cycle ergometer exercise test until volitional exhaustion. Stepwise linear regression was used to explore relationships between HbA1c and cardio-respiratory data with p ≤ 0.05. Furthermore, participants were divided into quartiles based on HbA1c levels and cardio-respiratory data were analysed by one-way ANOVA. Multiple regression analysis was performed to explore the relationships between changes in time to exhaustion and cardio-respiratory data. Data were adjusted for confounder.ResultsHbA1c was related to time to exhaustion and oxygen consumption at the power output elicited at the sub-maximal threshold of the heart rate turn point (r = 0.47, R2 = 0.22, p = 0.03). Significant differences were found at time to exhaustion between QI vs. QIV and at oxygen consumption at the power output elicited at the heart rate turn point between QI vs. QII and QI vs. QIV (p < 0.05). Changes in oxygen uptake, power output and in oxygen consumption at the power output elicited at the heart rate turn point and at maximum power output explained 55% of the variance in time to exhaustion (r = 0.74, R2 = 0.55, p < 0.01).ConclusionsPoor glycaemic control is related to less economical use of oxygen at sub-maximal work rates and an earlier time to exhaustion during cardio-pulmonary exercise testing. However, exercise training could have the same potential to counteract the influence of poor glycaemic control on functional capacity
New Limits on Doubly Charged Bileptons from CERN LEP Data and the Search at Future Electron-Positron and Electron-Photon Colliders
We show that the accumulated LEP-II data taken at 130 to 206 GeV
can establish more restrictive bounds on doubly charged bileptons couplings and
masses than any other experiment so far. We also analyze the discovery
potential of a prospective linear collider operating in both and modes.Comment: Revised version with 14 pages, 7 figures, RevTex. To appear in Phys.
Rev.
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