450 research outputs found
An Entourage Approach to the Contraction Principle in Uniform Spaces Endowed with a Graph
In this paper, we study Banach contractions in uniform spaces endowed with a
graph and give some sufficient conditions for a mapping to be a Picard
operator. Our main results generalize some results of [J. Jachymski, "The
contraction principle for mappings on a metric space with a graph", Proc. Amer.
Math. Soc. 136 (2008) 1359-1373] employing the basic entourages of the uniform
space.Comment: 20 page
Imaging and manipulating electrons in a 1D quantum dot with Coulomb blockade microscopy
Motivated by the recent experiments by the Westervelt group using a mobile
tip to probe the electronic state of quantum dots formed on a segmented
nanowire, we study the shifts in Coulomb blockade peak positions as a function
of the spatial variation of the tip potential, which can be termed "Coulomb
blockade microscopy". We show that if the tip can be brought sufficiently close
to the nanowire, one can distinguish a high density electronic liquid state
from a Wigner crystal state by microscopy with a weak tip potential. In the
opposite limit of a strongly negative tip potential, the potential depletes the
electronic density under it and divides the quantum wire into two partitions.
There the tip can push individual electrons from one partition to the other,
and the Coulomb blockade micrograph can clearly track such transitions. We show
that this phenomenon can be used to qualitatively estimate the relative
importance of the electron interaction compared to one particle potential and
kinetic energies. Finally, we propose that a weak tip Coulomb blockade
micrograph focusing on the transition between electron number N=0 and N=1
states may be used to experimentally map the one-particle potential landscape
produced by impurities and inhomogeneities.Comment: 4 pages 7 figure
The Effect of Flavonoid Naringenin on Contractile Response of Thoracic Aorta Isolated from Diabetic Rats
Abstract:
Background & Aims: Considering increasing incidence of cardiovascular disorders in diabetes mellitus and some evidence on antioxidant and antidiabetic potentials of naringenin, this study was conducted to evaluate the beneficial effects of 6-week administration of naringenin on contractile reactivity of isolated thoracic aorta in diabetic rats.
Methods: Male Wistar rats were divided into control, naringenin-treated control, diabetic and glibenclamide-treated, and naringenin-treated diabetic groups. For induction of diabetes, streptozotcin (STZ) was administered (60 mg/Kg). Naringenin (10 mg/kg) was administered i.p. one week after diabetes induction in every other day intervals for 6 weeks. Serum glucose level was measured before naringenin administration and at 6th week. Finally, contractile reactivity of thoracic aortic rings to KCl and phenylephrine (PE) was cumulatively determined.
Results: Serum glucose level at week 6 showed a significant decrease in naringenin-treated diabetic group compared to diabetics (P<0.01). In addition, naringenin-treated diabetic group showed a significantly lower contraction to PE (P<0.05) as compared to diabetic group and such significant reduction was also observed for KCl (P<0.05). Meanwhile, there was also a significant difference between control and naringenin-treated control groups regarding their contractile reactivity to PE (P<0.05).
Conclusion: Subchronic administration of naringenin for 6 weeks could exert an anti-hyperglycemic effect and lowers contractile responsiveness of thoracic aorta rings to KCl and phenylephrine.
Keywords: Naringenin, Diabetes mellitus, Aorta, Contractilit
Symmetric Operation of the Resonant Exchange Qubit
We operate a resonant exchange qubit in a highly symmetric triple-dot
configuration using IQ-modulated RF pulses. At the resulting three-dimensional
sweet spot the qubit splitting is an order of magnitude less sensitive to all
relevant control voltages, compared to the conventional operating point, but we
observe no significant improvement in the quality of Rabi oscillations. For
weak driving this is consistent with Overhauser field fluctuations modulating
the qubit splitting. For strong driving we infer that effective voltage noise
modulates the coupling strength between RF drive and the qubit, thereby
quickening Rabi decay. Application of CPMG dynamical decoupling sequences
consisting of up to n = 32 {\pi} pulses significantly prolongs qubit coherence,
leading to marginally longer dephasing times in the symmetric configuration.
This is consistent with dynamical decoupling from low frequency noise, but
quantitatively cannot be explained by effective gate voltage noise and
Overhauser field fluctuations alone. Our results inform recent strategies for
the utilization of partial sweet spots in the operation and long-distance
coupling of triple-dot qubits.Comment: 6 pages, 5 figure
Negative spin exchange in a multielectron quantum dot
By operating a one-electron quantum dot (fabricated between a multielectron
dot and a one-electron reference dot) as a spectroscopic probe, we study the
spin properties of a gate-controlled multielectron GaAs quantum dot at the
transition between odd and even occupation number. We observe that the
multielectron groundstate transitions from spin-1/2-like to singlet-like to
triplet-like as we increase the detuning towards the next higher charge state.
The sign reversal in the inferred exchange energy persists at zero magnetic
field, and the exchange strength is tunable by gate voltages and in-plane
magnetic fields. Complementing spin leakage spectroscopy data, the inspection
of coherent multielectron spin exchange oscillations provides further evidence
for the sign reversal and, inferentially, for the importance of non-trivial
multielectron spin exchange correlations.Comment: 8 pages, including 4 main figures and 2 supplementary figurure
Noise suppression using symmetric exchange gates in spin qubits
We demonstrate a substantial improvement in the spin-exchange gate using
symmetric control instead of conventional detuning in GaAs spin qubits, up to a
factor-of-six increase in the quality factor of the gate. For symmetric
operation, nanosecond voltage pulses are applied to the barrier that controls
the interdot potential between quantum dots, modulating the exchange
interaction while maintaining symmetry between the dots. Excellent agreement is
found with a model that separately includes electrical and nuclear noise
sources for both detuning and symmetric gating schemes. Unlike exchange control
via detuning, the decoherence of symmetric exchange rotations is dominated by
rotation-axis fluctuations due to nuclear field noise rather than direct
exchange noise.Comment: 5 pages main text (4 figures) plus 5 pages supplemental information
(3 figures
Spectrum of the Nuclear Environment for GaAs Spin Qubits
Using a singlet-triplet spin qubit as a sensitive spectrometer of the GaAs
nuclear spin bath, we demonstrate that the spectrum of Overhauser noise agrees
with a classical spin diffusion model over six orders of magnitude in
frequency, from 1 mHz to 1 kHz, is flat below 10 mHz, and falls as for
frequency Hz. Increasing the applied magnetic field from
0.1 T to 0.75 T suppresses electron-mediated spin diffusion, which decreases
spectral content in the region and lowers the saturation frequency,
each by an order of magnitude, consistent with a numerical model. Spectral
content at megahertz frequencies is accessed using dynamical decoupling, which
shows a crossover from the few-pulse regime ( -pulses),
where transverse Overhauser fluctuations dominate dephasing, to the many-pulse
regime ( -pulses), where longitudinal Overhauser
fluctuations with a spectrum dominate.Comment: 6 pages, 4 figures, 8 pages of supplementary material, 5
supplementary figure
Fast spin exchange between two distant quantum dots
The Heisenberg exchange interaction between neighboring quantum dots allows
precise voltage control over spin dynamics, due to the ability to precisely
control the overlap of orbital wavefunctions by gate electrodes. This allows
the study of fundamental electronic phenomena and finds applications in quantum
information processing. Although spin-based quantum circuits based on
short-range exchange interactions are possible, the development of scalable,
longer-range coupling schemes constitutes a critical challenge within the
spin-qubit community. Approaches based on capacitative coupling and
cavity-mediated interactions effectively couple spin qubits to the charge
degree of freedom, making them susceptible to electrically-induced decoherence.
The alternative is to extend the range of the Heisenberg exchange interaction
by means of a quantum mediator. Here, we show that a multielectron quantum dot
with 50-100 electrons serves as an excellent mediator, preserving speed and
coherence of the resulting spin-spin coupling while providing several
functionalities that are of practical importance. These include speed (mediated
two-qubit rates up to several gigahertz), distance (of order of a micrometer),
voltage control, possibility of sweet spot operation (reducing susceptibility
to charge noise), and reversal of the interaction sign (useful for dynamical
decoupling from noise).Comment: 6 pages including 4 figures, plus 8 supplementary pages including 5
supplementary figure
A Dyadic Approach to Understanding Associations Between Job Stress, Marital Quality, and Dyadic Coping for Dual-Career Couples in Iran
In Iran, dual-career couples face many stressors due to their demands of balancing work and family. Moreover, the experience of this stress can negatively affect partners’ martial quality. Recent studies have shown the positive impact of dyadic coping on well-being; however, a majority of this research has been conducted with Western cultures. As such, there is a dearth of literature on understanding how supportive and common dyadic coping may have a positive association with work-family stress for couples in Iran. Using a sample of 206 heterosexual dual-career couples from Iran, this study examines the associations between job stress and marital quality, and possible moderating effects of common and perceived partner supportive dyadic coping. As predicted, job stress was negatively associated with marital quality, and this association with further moderated by gender, such that women who experienced greater job stress also reported lower marital quality. Additionally, dyadic coping moderated the association between job stress and marital quality. Common dyadic coping attenuated the negative association between job stress and marital quality. The findings shed light on the possible beneficial effects of teaching supportive and common dyadic coping techniques to dual-career couples in Iran
- …