2,796 research outputs found
Exponential torsion growth for random 3-manifolds
We show that a random 3-manifold with positive first Betti number admits a tower of cyclic covers with exponential torsion growth
On stratification for spaces with Noetherian mod cohomology
Let be a topological space with Noetherian mod cohomology and let be the commutative ring spectrum of -valued cochains on . The goal of this paper is to exhibit conditions under which the category of module spectra on is stratified in the sense of Benson, Iyengar, Krause, providing a classification of all its localizing subcategories. We establish stratification in this sense for classifying spaces of a large class of topological groups including Kac--Moody groups as well as whenever admits an -space structure. More generally, using Lannes' theory we prove that stratification for is equivalent to a condition that generalizes Chouinard's theorem for finite groups. In particular, this relates the generalized telescope conjecture in this setting to a question in unstable homotopy theory
Quantum Phase Tomography of a Strongly Driven Qubit
The interference between repeated Landau-Zener transitions in a qubit swept
through an avoided level crossing results in Stueckelberg oscillations in qubit
magnetization. The resulting oscillatory patterns are a hallmark of the
coherent strongly-driven regime in qubits, quantum dots and other two-level
systems. The two-dimensional Fourier transforms of these patterns are found to
exhibit a family of one-dimensional curves in Fourier space, in agreement with
recent observations in a superconducting qubit. We interpret these images in
terms of time evolution of the quantum phase of qubit state and show that they
can be used to probe dephasing mechanisms in the qubit.Comment: 5 pgs, 4 fg
Optical-conductivity sum rule in cuprates and unconventional charge density waves: a short review
We begin with an overview of the experimental results for the temperature and
doping dependences of the optical-conductivity spectral weight in cuprate
superconductors across the whole phase diagram. Then we discuss recent attempts
to explain the observed behavior of the spectral weight using reduced and full
models with unconventional charge-density waves.Comment: 17 pages, RevTeX4, 4 EPS figures; Invited paper for a special issue
of Low Temperature Physics dedicated to the 20th anniversary of HTS
Collective motional resonances and instabilities of an electron cloud stored in a Penning trap
We have experimentally investigated the behavior of an electron cloud confined in a Penning trap at weak superimposed magnetic fields. Exciting the motional frequencies of the electrons by an external drive field we found the axial mode split into two components which were identified as center-of-mass and individual electron oscillations. When the trapping potential was varied, rapid electron loss appeared at numerous values of the applied voltage. They are determined by the relation n z ω z + n m ω m =ω c . ω z ,ω m ,ω c are the axial, magnetron, and cyclotron frequency of the trapped electrons, respectively. The reason for this loss is attributed to higher order contributions to the ideal quadrupole trapping potential
A Bespoke Kinect Stepping Exergame for Improving Physical and Cognitive Function in Older People: A Pilot Study
© 2016 Mary Ann Liebert, Inc. Background: Systematic review evidence has shown that step training reduces the number of falls in older people by half. This study investigated the feasibility and effectiveness of a bespoke Kinect stepping exergame in an unsupervised home-based setting. Materials and Methods: An uncontrolled pilot trial was conducted in 12 community-dwelling older adults (mean age 79.3 ± 8.7 years, 10 females). The stepping game comprised rapid stepping, attention, and response inhibition. Participants were recommended to exercise unsupervised at home for a minimum of three 20-minute sessions per week over the 12-week study period. The outcome measures were choice stepping reaction time (CSRT) (main outcome measure), standing balance, gait speed, five-time sit-to-stand (STS), timed up and go (TUG) performance, and neuropsychological function (attention: letter-digit and executive function:Stroop tests) assessed at baseline, 4 weeks, 8 weeks, and trial end (12 weeks). Results: Ten participants (83%) completed the trial and reassessments. A median 8.2 20-minute sessions were completed and no adverse events were reported. Across the trial period, participants showed significant improvements in CSRT (11%), TUG (13%), gait speed (29%), standing balance (7%), and STS (24%) performance (all P < 0.05). There were also nonsignificant, but meaningful, improvements for the letter-digit (13%) and Stroop tests (15%). Conclusions: This study found that a bespoke Kinect step training program was safe and feasible for older people to undertake unsupervised at home and led to improvements in stepping, standing balance, gait speed, and mobility. The home-based step training program could therefore be included in exercise programs designed to prevent falls
Deformation of the Fermi surface in the extended Hubbard model
The deformation of the Fermi surface induced by Coulomb interactions is
investigated in the t-t'-Hubbard model. The interplay of the local U and
extended V interactions is analyzed. It is found that exchange interactions V
enhance small anisotropies producing deformations of the Fermi surface which
break the point group symmetry of the square lattice at the Van Hove filling.
This Pomeranchuck instability competes with ferromagnetism and is suppressed at
a critical value of U(V). The interaction V renormalizes the t' parameter to
smaller values what favours nesting. It also induces changes on the topology of
the Fermi surface which can go from hole to electron-like what may explain
recent ARPES experiments.Comment: 5 pages, 4 ps figure
Strategies to capture biotechnology opportunities in Chile
Two complementary strategies are proposed to help develop the
biotechnology industry in Chile. The objectives of such propositions
are based on identifying business opportunities, which can be
transformed into biotechnology projects that complement the competitive
advantages of the most active areas of the Chilean economy. As a
result, the establishment of these initiatives may create the proper
business environment where good information, investors'safeguards and
economic incentives would be provided to encourage investors to support
new biotechnology ventures focused on mining, aquaculture, forestry, as
well as wine and fruit production. In addition, a complete description
of the Chilean biotechnology industry is provided. Amongst other
characteristics, this report shows that the industry lacks financial
support from venture capital and foreign investors, has a relatively
modest proportion of highly qualified employees that work in Research
and Development, presents insufficient patent productivity and is
mostly regulated in terms of the use of GMOs
Impact of time-ordered measurements of the two states in a niobium superconducting qubit structure
Measurements of thermal activation are made in a superconducting, niobium
Persistent-Current (PC) qubit structure, which has two stable classical states
of equal and opposite circulating current. The magnetization signal is read out
by ramping the bias current of a DC SQUID. This ramping causes time-ordered
measurements of the two states, where measurement of one state occurs before
the other. This time-ordering results in an effective measurement time, which
can be used to probe the thermal activation rate between the two states.
Fitting the magnetization signal as a function of temperature and ramp time
allows one to estimate a quality factor of 10^6 for our devices, a value
favorable for the observation of long quantum coherence times at lower
temperatures.Comment: 14 pages, 4 figure
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