3,833 research outputs found
Coherent Control of Trapped Bosons
We investigate the quantum behavior of a mesoscopic two-boson system produced
by number-squeezing ultracold gases of alkali metal atoms. The quantum Poincare
maps of the wavefunctions are affected by chaos in those regions of the phase
space where the classical dynamics produces features that are comparable to
hbar. We also investigate the possibility for quantum control in the dynamics
of excitations in these systems. Controlled excitations are mediated by pulsed
signals that cause Stimulated Raman Adiabatic passage (STIRAP) from the ground
state to a state of higher energy. The dynamics of this transition is affected
by chaos caused by the pulses in certain regions of the phase space. A
transition to chaos can thus provide a method of controlling STIRAP.Comment: 17 figures, Appended a paragraph on section 1 and explained details
behind the hamiltonian on section
Olfactory receptors in the melon fly Dacus cucurbitae and the oriental fruit fly Dacus dorsalis
Early diffusion evidence of retrograde transsynaptic degeneration in the human visual system
We investigated whether diffusion tensor imaging (DTI) indices of white matter integrity would offer early markers of retrograde transsynaptic degeneration (RTD) in the visual system after stroke
Objective: We investigated whether diffusion tensor imaging (DTI) indices of white matter integrity
would offer early markers of retrograde transsynaptic degeneration (RTD) in the visual system
after stroke.
Methods: We performed a prospective longitudinal analysis of the sensitivity of DTI markers of
optic tract health in 12 patients with postsynaptic visual pathway stroke, 12 stroke controls,
and 28 healthy controls. We examined group differences in (1) optic tract fractional anisotropy
(FA-asymmetry), (2) perimetric measures of visual impairment, and (3) the relationship between
FA-asymmetry and perimetric assessment.
Results: FA-asymmetry was higher in patients with visual pathway lesions than in control groups.
These differences were evident 3 months from the time of injury and did not change significantly
at 12 months. Perimetric measures showed evidence of impairment in participants with visual
pathway stroke but not in control groups. A significant association was observed between
FA-asymmetry and perimetric measures at 3 months, which persisted at 12 months.
Conclusions: DTI markers of RTD are apparent 3 months from the time of injury. This represents
the earliest noninvasive evidence of RTD in any species. Furthermore, these measures associate
with measures of visual impairment. DTI measures offer a reproducible, noninvasive, and sensitive
method of investigating RTD and its role in visual impairment
Seeing What Others Miss: A Study of Women Entrepreneurs in High-Growth Startups
A pressing question in entrepreneurial research is where opportunities come from. Prior research indicates that some opportunities stem from known parameters and outcomes; some are discovered through engagement with unknown but knowable factors; and others are unknowable until brought into being through a creative process. This paper explores the second and more prevailing view in entrepreneurial research – that individuals discover business opportunity – and examines how high-growth entrepreneurs perceive opportunity through engagement with the world. Survey results, based on responses from 165 women entrepreneurs in high-growth startups, indicate that individuals with a strong discover mindset act and think in ways that support opportunity perception. Coupled with a belief in her abilities, the entrepreneur is more likely to move from opportunity perception to new venture creation. Results from semi-structured interviews with women from the same population elucidate the survey findings and yield implications for entrepreneurial theory and practice
Bichromatic Slowing of Metastable Helium
We examine two approaches for significantly extending the velocity range of
the optical bichromatic force (BCF), to make it useful for laser deceleration
of atomic and molecular beams. First, we present experimental results and
calculations for BCF deceleration of metastable helium using very large BCF
detunings, and discuss the limitations of this approach. We consider in detail
the constraints, both inherent and practical, that set the usable upper limit
of the BCF. We then show that a more promising approach is to utilize a BCF
profile with a relatively small velocity range in conjunction with chirped
Doppler shifts, to keep the force resonant with the atoms as they are slowed.
In an initial experimental test of this chirped BCF method, helium atoms are
slowed by m/s using a BCF profile with a velocity width of m/s. Straightforward scaling of the present results indicates that a
decelerator for He* capable of loading a magneto-optical trap (MOT) can yield a
brightness comparable to a much larger Zeeman slower.Comment: 11 pages, 9 figures. Published in Phys. Rev.
Distinguishing entrepreneurial approaches to opportunity perception
Purpose – Whether opportunities are discovered or created by entrepreneurs is a foundational question in entrepreneurship research. The purpose of this paper is to examine women entrepreneurs in high-growth new ventures and explore the cognitive resources that distinguish between three approaches to opportunity perception: opportunity discovery; opportunity creation; and a combined discover-create (ambidextrous) approach.
Design/methodology/approach – Using questionnaire responses from 165 women entrepreneurs in highgrowth new ventures, K-means clustering was used to determine three approaches to opportunity perception. The cognitive resources associated with each approach were then identified using multiple discriminant analysis. Finally, multivariate analysis of variance was conducted to examine the relationship between opportunity perception and growth expectations.
Findings – These results demonstrate different approaches to opportunity perception among entrepreneurs in high-growth new ventures, the cognitive resources that reinforce each approach, and the expected new venture growth outcomes.
Research limitations/implications – The findings offer insight on the cognitive origins of opportunity perception by empirically identifying distinct approaches to opportunity perception and the cognitive resources that underlie each. The study relies on a unique sample of entrepreneurs to understand complex cognitive phenomenon.
Practical implications – Understanding the effects that cognitive factors have on opportunity perception provides direction for current and aspiring entrepreneurs. The findings and instrument may be used for professional development and to inform educational strategies.
Originality/value – The findings offer important contributions to entrepreneurial theory and practice by addressing repeated calls for research that examines the cognitive antecedents enabling opportunity formation (discovery, creation or both). This manuscript empirically does so, while opening up possibilities for future research
Cybercrime: Issues and challenges in the United States
Chief Judge B. Lynn Winmill, David L. Metcalf and Michael E. Band provide a succinct introduction to the use of computers and the internet, illustrating some of the problems that have accompanied the internet, before providing an outline of the response by successive administrations. The relevant legislation is set out, with a discussion of the issues relating to electronic evidence, hearsay, authentication, and search and seizure in the United States
Loss of molecules in magneto-electrostatic traps due to nonadiabatic transitions
We analyze the dynamics of a paramagnetic, dipolar molecule in a generic
"magneto-electrostatic'' trap where both magnetic and electric fields may be
present. The potential energy that governs the dynamics of the molecules is
found using a reduced molecular model that incorporates the main features of
the system. We discuss the shape of the trapping potentials for different field
geometries, as well as the possibility of nonadiabatic transitions to untrapped
states, i.e., the analog of Majorana transitions in a quadrupole magnetic
atomic trap. Maximizing the lifetime of molecules in a trap is of great concern
in current experiments, and we assess the effect of nonadiabatic transitions on
obtainable trap lifetimes.Comment: 13 pages, 6 figure
The Detection of Pure Dark Matter Objects with Bent Multiply Imaged Radio Jets
When a gravitational lens produces two or more images of a quasar's radio jet
the images can be compared to reveal the presence of small structures along one
or more of the lines of sight. If mass is distributed smoothly on scales of <~
10^7 Msun independent bends in the jet images on milli-arcsecond scales will
not be produced. All three of the well collimated multiply imaged radio jets
that have been mapped on milli-arcsecond scales show some evidence of
independent bends in their images. Using existing data we model the lens system
B1152+199 and show that it likely contains a substructure of mass ~10^5 - 10^7
h^-1 Msun or a velocity dispersion of ~ 10 km/s. An alternative explanation is
that an intrinsic bend in the jet is undetected in one image and magnified in
the other. This explanation is disfavored and future observations could remove
any ambiguity that remains. The probability of a radio jet being bent by small
scale structure both inside and outside of the host lens is then investigate.
The known populations of dwarf galaxies and globular clusters are far too small
to make this probability acceptable. A previously unknown population of massive
dark objects is needed. The standard Cold Dark Matter (CDM) model might be able
to account for the observations if small mass halos are sufficiently compact.
In other cosmological models where small scale structure is suppressed, such as
standard Warm Dark Matter (WDM), the observed bent jets would be very unlikely
to occur.Comment: Significantly improved and extended - Better comparison with
observations and a more complete treatment of alternative explanations that
do not require substructure. Some small errors are corrected. 16 pages, 4
figures, submitted to Ap
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