155 research outputs found
Location and thermal evolution of the pseudogap due to spin fluctuations
We study pseudogap behavior in a metal near a spin density wave (SDW)
instability due to thermal magnetic fluctuations. We consider the
Hubbard model on a square lattice at a finite doping, at intermediate coupling
strength, and analyze the thermal evolution of the electron spectral function
between a SDW ordered state at low temperatures and a normal Fermi liquid at
high temperatures. We argue that for proper description of the pseudogap one
needs to sum up infinite series of diagrams for both the fermionic self-energy
and the SDW order parameter in the SDW state or the magnetic correlation length
in the paramagnetic state. We use eikonal approach to sum up an infinite series
of diagrammatic contributions from thermal fluctuations. Earlier studies found
that in the SDW state, the spectral function of a hot
fermion at a finite is exponentially small below the energy scale , which scales with SDW order and vanishes at the ordering temperature
, and has a hump at a larger frequency , comparable to
the zero-temperature SDW gap . We argue that the hump, which we
associate with the pseudogap, survives in some range above . We show
that this range is split by regions of strong and weak pseudogap behavior. In
the first region, is weakly temperature dependent, despite
that it comes from thermal fluctuations. Such a behavior has been seen in
numerical studies of the Hubbard model. We show that to obtain it, one needs to
go beyond the one-loop approximation and sum up the infinite series of
diagrams. In the second regime, decreases with increasing
and eventually vanishes. We further argue that a magnetic pseudogap at a finite
emerges only if the ground state is magnetically ordered. We present the
phase diagram and apply the results to high- cuprates.Comment: 22+3 pages, 16 figure
Performance Analysis of Discrete-Phase-Shifter IRS-aided Amplify-and-Forward Relay Network
As a new technology to reconfigure wireless communication environment by
signal reflection controlled by software, intelligent reflecting surface (IRS)
has attracted lots of attention in recent years. Compared with conventional
relay system, the relay system aided by IRS can effectively reduce the cost and
energy consumption, and significantly enhance the system performance. However,
the phase quantization error generated by IRS with discrete phase shifter may
degrade the receiving performance of the receiver. To analyze the performance
loss caused by IRS phase quantization error, based on the law of large numbers
and Rayleigh distribution, the closed-form expressions for the signal-to-noise
ratio (SNR) performance loss and achievable rate of the IRS-aided
amplify-and-forward (AF) relay network, which are related to the number of
phase shifter quantization bits, are derived under the line-of-sight (LoS)
channels and Rayleigh channels, respectively. Moreover, their approximate
performance loss closed-form expressions are also derived based on the Taylor
series expansion. Simulation results show that the performance losses of SNR
and achievable rate decrease with the number of quantization bits increases
gradually. When the number of quantization bits is larger than or equal to 3,
the SNR performance loss of the system is smaller than 0.23dB, and the
achievable rate loss is less than 0.04bits/s/Hz, regardless of the LoS channels
or Rayleigh channels
Three Efficient Beamforming Methods for Hybrid IRS plus AF Relay-aided Metaverse
In this paper, an optimization problem is formulated to maximize
signal-to-noise ratio (SNR) by jointly optimizing the beamforming matrix at AF
relay and the reflecting coefficient matrices at IRS subject to the constraints
of transmit power budgets at the base station (BS)/AF relay/hybrid IRS and that
of unit-modulus for passive IRS phase shifts. To achieve high rate performance
and extend the coverage range, a high-performance method based on semidefinite
relaxation and fractional programming (HP-SDR-FP) algorithm is presented. Due
to its extremely high complexity, a low-complexity method based on successive
convex approximation and FP (LC-SCA-FP) algorithm is put forward. To further
reduce the complexity, a lower-complexity method based on whitening filter,
general power iterative and generalized Rayleigh-Ritz (WF-GPI-GRR) is proposed,
where different from the above two methods, it is assumed that the amplifying
coefficient of each active IRS element is equal, and the corresponding
analytical solution of the amplifying coefficient can be obtained according to
the transmit powers at AF relay and hybrid IRS. Simulation results show that
the proposed three methods can greatly improve the rate performance compared to
the existing technology-aided metaverse, such as the passive IRS plus AF
relay-aided metaverse and only AF relay-aided metaverse. In particular, a 50.0%
rate gain over the existing technology-aided metaverse is approximately
achieved in the high power budget region of hybrid IRS. Moreover, it is
verified that the proposed three efficient beamforming methods have an
increasing order in rate performance: WF-GPI-GRR, LC-SCA-FP and HP-SDR-FP
Treating depressive disorders with the unified protocol: A preliminary randomized evaluation.
OBJECTIVES: This study aims to examine the efficacy of the Unified Protocol for Transdiagnostic Treatment of Emotional Disorders (UP) for individuals diagnosed with a depressive disorder. METHOD: Participants included 44 adults who met criteria for major depressive disorder, persistent depressive disorder, or another specified depressive disorder according to the Anxiety Disorder Interview Schedule (ADIS). These individuals represent a subset of patients from a larger clinical trial comparing the UP to single-disorder protocols (SDPs) for discrete anxiety disorders and a waitlist control (WLC) condition (Barlow et al., 2017); inclusion criteria for the parent study required participants to have a principal anxiety disorder. RESULTS: Significant reductions in depressive symptoms were observed within the UP condition across clinician-rated and self-report measures of depression from baseline to post-treatment, as well as to the 12-month follow-up assessment. Compared to the WLC group, individuals in the UP condition demonstrated significantly lower levels on our continuous, clinician-rated measure of depressive symptoms at post-treatment. There were no differences between the UP and SDP conditions on depressive symptoms at post-treatment or at the 12-month follow-up timepoint. CONCLUSIONS: In this exploratory set of analyses, the UP evidenced efficacy for reduction of depressive symptoms, adding to the growing support for its utility in treating depression.R01 MH090053 - NIMH NIH HHSAccepted manuscrip
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