6,979 research outputs found
The Universe and The Quantum Computer
It is first pointed out that there is a common mathematical model for the
universe and the quantum computer. The former is called the histories approach
to quantum mechanics and the latter is called measurement based quantum
computation. Although a rigorous concrete model for the universe has not been
completed, a quantum measure and integration theory has been developed which
may be useful for future progress. In this work we show that the quantum
integral is the unique functional satisfying certain basic physical and
mathematical principles. Since the set of paths (or trajectories) for a quantum
computer is finite, this theory is easier to treat and more developed. We
observe that the sum of the quantum measures of the paths is unity and the
total interference vanishes. Thus, constructive interference is always balanced
by an equal amount of destructive interference. As an example we consider a
simplified two-slit experimentComment: 15 pages, IQSA 2010 proceeding
Unambiguous determination of spin dephasing times in ZnO
Time-resolved magneto-optics is a well-established optical pump probe
technique to generate and to probe spin coherence in semiconductors. By this
method, spin dephasing times T_2^* can easily be determined if their values are
comparable to the available pump-probe-delays. If T_2^* exceeds the laser
repetition time, however, resonant spin amplification (RSA) can equally be used
to extract T_2^*. We demonstrate that in ZnO these techniques have several
tripping hazards resulting in deceptive values for T_2^* and show how to avoid
them. We show that the temperature dependence of the amplitude ratio of two
separate spin species can easily be misinterpreted as a strongly temperature
dependent T_2^* of a single spin ensemble, while the two spin species have
T_2^* values which are nearly independent of temperature. Additionally,
consecutive pump pulses can significantly diminish the spin polarization, which
remains from previous pump pulses. While this barely affects T_2^* values
extracted from delay line scans, it results in seemingly shorter T_2^* values
in RSA.Comment: 11 pages, 10 figure
Predictors of Venous Thromboembolism in Patients with Advanced Common Solid Cancers
There is uncertainty about risk heterogeneity for venous thromboembolism (VTE) in older
patients with advanced cancer and whether patients can be stratified according to VTE risk. We performed a retrospective cohort study of the linked Medicare-Surveillance, Epidemiology, and End Results cancer registry in older patients with advanced cancer of lung, breast, colon, prostate, or pancreas diagnosed between 1995–1999. We used survival analysis with demographics, comorbidities, and tumor characteristics/treatment as independent variables. Outcome was VTE diagnosed at least one month after cancer diagnosis. VTE rate was highest in the first year (3.4%). Compared to prostate cancer (1.4 VTEs/100 person-years), there was marked variability in VTE risk (hazard ratio (HR) for male-colon cancer 3.73 (95% CI 2.1–6.62), female-colon cancer HR 6.6 (3.83–11.38), up to female-pancreas cancer HR 21.57
(12.21–38.09). Stage IV cancer and chemotherapy resulted in higher risk (HRs 1.75 (1.44–2.12) and 1.31 (1.0–1.57), resp.). Stratifying the cohort by cancer type and stage using recursive partitioning analysis yielded five groups of VTE rates (nonlocalized prostate cancer 1.4 VTEs/100 person-years, to nonlocalized pancreatic cancer 17.4 VTEs/100 patient-years). In a high-risk population with advanced cancer, substantial variability in VTE risk exists, with notable differences according to cancer type and stage
Flat-space scattering and bulk locality in the AdS/CFT correspondence
The large radius limit in the AdS/CFT correspondence is expected to provide a
holographic derivation of flat-space scattering amplitudes. This suggests that
questions of locality in the bulk should be addressed in terms of properties of
the S-matrix and their translation into the conformal field theory. There are,
however, subtleties in this translation related to generic growth of amplitudes
near the boundary of anti de-Sitter space. Flat space amplitudes are recovered
after a delicate projection of CFT correlators onto normal-mode frequencies of
AdS. Once such amplitudes are obtained from the CFT, possible criteria for
approximate bulk locality include bounds on growth of amplitudes at high
energies and reproduction of semiclassical gravitational scattering at long
distances.Comment: 25 pages, harvmac. v2: Very minor corrections to eqs. v3: Minor
improvements of discussion of locality bounds and string scattering v4. Typos
fixe
Spontaneous emission from large quantum dots in nanostructures: exciton-photon interaction beyond the dipole approximation
We derive a rigorous theory of the interaction between photons and spatially
extended excitons confined in quantum dots in inhomogeneous photonic materials.
We show that, beyond the dipole approximation, the radiative decay rate is
proportional to a non-local interaction function, which describes the
interaction between light and spatially extended excitons. In this regime,
light and matter degrees of freedom cannot be separated and a complex interplay
between the nanostructured optical environment and the exciton envelope
function emerges. We illustrate this by specific examples and derive a series
of important analytical relations, which are useful for applying the formalism
to practical problems. In the dipole limit, the decay rate is proportional to
the projected local density of optical states and we obtain the strong and weak
confinement regimes as special cases.Comment: 14 pages, 4 figure
Interacting Dipoles from Matrix Formulation of Noncommutative Gauge Theories
We study the IR behavior of noncommutative gauge theory in the matrix
formulation. We find that in this approach, the nature of the UV/IR mixing is
easily understood, which allows us to perform a reliable calculation of the
quantum effective action for the long wavelength modes of the noncommutative
gauge field. At one loop, we find that our description is weakly coupled only
in the supersymmetric theory. At two loops, we find non-trivial interaction
terms suggestive of dipole degrees of freedom. These dipoles exhibit a channel
duality reminiscent of string theory.Comment: LaTeX 11 pages, 4 figures; v.2 minor changes and some references
added; v.3 many more technical details added and significantly different
presentation, use REVTeX 4, to appear in PR
Local charge and spin currents in magnetothermal landscapes
A scannable laser beam is used to generate local thermal gradients in
metallic (Co2FeAl) or insulating (Y3Fe5O12) ferromagnetic thin films. We study
the resulting local charge and spin currents that arise due to the anomalous
Nernst effect (ANE) and the spin Seebeck effect (SSE), respectively. In the
local ANE experiments, we detect the voltage in the Co2FeAl thin film plane as
a function of the laser spot position and external magnetic field magnitude and
orientation. The local SSE effect is detected in a similar fashion by
exploiting the inverse spin Hall effect in a Pt layer deposited on top of the
Y3Fe5O12. Our findings establish local thermal spin and charge current
generation as well as spin caloritronic domain imaging
The EDAM Project: Mining Atmospheric Aerosol Datasets
Data mining has been a very active area of research in the database, machine learning, and mathematical programming communities in recent years. EDAM (Exploratory Data Analysis and Management) is a joint project between researchers in Atmospheric Chemistry and Computer Science at Carleton College and the University of Wisconsin-Madison that aims to develop data mining techniques for advancing the state of the art in analyzing atmospheric aerosol datasets. There is a great need to better understand the sources, dynamics, and compositions of atmospheric aerosols. The traditional approach for particle measurement, which is the collection of bulk samples of particulates on filters, is not adequate for studying particle dynamics and real-time correlations. This has led to the development of a new generation of real-time instruments that provide continuous or semi-continuous streams of data about certain aerosol properties. However, these instruments have added a significant level of complexity to atmospheric aerosol data, and dramatically increased the amounts of data to be collected, managed, and analyzed. Our abilit y to integrate the data from all of these new and complex instruments now lags far behind our data-collection capabilities, and severely limits our ability to understand the data and act upon it in a timely manner. In this paper, we present an overview of the EDAM project. The goal of the project, which is in its early stages, is to develop novel data mining algorithms and approaches to managing and monitoring multiple complex data streams. An important objective is data quality assurance, and real-time data mining offers great potential. The approach that we take should also provide good techniques to deal with gas-phase and semi-volatile data. While atmospheric aerosol analysis is an important and challenging domain that motivates us with real problems and serves as a concrete test of our results, our objective is to develop techniques that have broader applicability, and to explore some fundamental challenges in data mining that are not specific to any given application domain
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