24,583 research outputs found
On the propagation of semiclassical Wigner functions
We establish the difference between the propagation of semiclassical Wigner
functions and classical Liouville propagation. First we re-discuss the
semiclassical limit for the propagator of Wigner functions, which on its own
leads to their classical propagation. Then, via stationary phase evaluation of
the full integral evolution equation, using the semiclassical expressions of
Wigner functions, we provide the correct geometrical prescription for their
semiclassical propagation. This is determined by the classical trajectories of
the tips of the chords defined by the initial semiclassical Wigner function and
centered on their arguments, in contrast to the Liouville propagation which is
determined by the classical trajectories of the arguments themselves.Comment: 9 pages, 1 figure. To appear in J. Phys. A. This version matches the
one set to print and differs from the previous one (07 Nov 2001) by the
addition of two references, a few extra words of explanation and an augmented
figure captio
Theoretical investigation of moir\'e patterns in quantum images
Moir\'e patterns are produced when two periodic structures with different
spatial frequencies are superposed. The transmission of the resulting structure
gives rise to spatial beatings which are called moir\'e fringes. In classical
optics, the interest in moir\'e fringes comes from the fact that the spatial
beating given by the frequency difference gives information about details(high
spatial frequency) of a given spatial structure. We show that moir\'e fringes
can also arise in the spatial distribution of the coincidence count rate of
twin photons from the parametric down-conversion, when spatial structures with
different frequencies are placed in the path of each one of the twin beams. In
other words,we demonstrate how moir\'e fringes can arise from quantum images
Gender Matters! Analyzing Global Cultural Gender Preferences for Venues Using Social Sensing
Gender differences is a phenomenon around the world actively researched by
social scientists. Traditionally, the data used to support such studies is
manually obtained, often through surveys with volunteers. However, due to their
inherent high costs because of manual steps, such traditional methods do not
quickly scale to large-size studies. We here investigate a particular aspect of
gender differences: preferences for venues. To that end we explore the use of
check-in data collected from Foursquare to estimate cultural gender preferences
for venues in the physical world. For that, we first demonstrate that by
analyzing the check-in data in various regions of the world we can find
significant differences in preferences for specific venues between gender
groups. Some of these significant differences reflect well-known cultural
patterns. Moreover, we also gathered evidence that our methodology offers
useful information about gender preference for venues in a given region in the
real world. This suggests that gender and venue preferences observed may not be
independent. Our results suggests that our proposed methodology could be a
promising tool to support studies on gender preferences for venues at different
spatial granularities around the world, being faster and cheaper than
traditional methods, besides quickly capturing changes in the real world
Mobile solutions in depression: Enhancing communication with patients using an SMS-based intervention
Mobile solutions, namely the ones based on the Short Message Service (SMS), can play an important role in enhancing communication with patients with depression, between consultations, allowing the delivery of supportive messages or reminders. This paper presents an overview on this topic and describes a 4-stage study aiming to better understand the mHealth scenario in depression, specifically regarding the use of messaging services. The four stages comprised: (i) a diagnosis of perspectives and practices; (ii) a 6-weeks SMS intervention plan; (iii) a prototype of a digital application to support patients' follow-up and interaction; (iv) and a survey with physicians on digital experience and predisposition to use the prototype. Results underline the potential of the use of messaging systems and digital solutions to improve communication with patients with depression and point the benefits of blended-interventions (combining personal contact and SMSs, as an adjunct/complement to regular treatment). Further researched is needed, particular regarding the adjustment of these solutions to specific target groups
Three-dimensional Dirac oscillator in a thermal bath
The thermal properties of the three-dimensional Dirac oscillator are
considered. The canonical partition function is determined, and the
high-temperature limit is assessed. The degeneracy of energy levels and their
physical implications on the main thermodynamic functions are analyzed,
revealing that these functions assume values greater than the one-dimensional
case. So that at high temperatures, the limit value of the specific heat is
three times bigger.Comment: 9 pages, 4 figures. Text improved, references added. Revised to match
accepted version in Europhysics Letters
Chromosome Segregation Is Biased by Kinetochore Size
Chromosome missegregation during mitosis or meiosis is a hallmark of cancer and the main cause of prenatal death in humans. The gain or loss of specific chromosomes is thought to be random, with cell viability being essentially determined by selection. Several established pathways including centrosome amplification, sister-chromatid cohesion defects, or a compromised spindle assembly checkpoint can lead to chromosome missegregation. However, how specific intrinsic features of the kinetochore—the critical chromosomal interface with spindle microtubules—impact chromosome segregation remains poorly understood. Here we used the unique cytological attributes of female Indian muntjac, the mammal with the lowest known chromosome number (2n = 6), to characterize and track individual chromosomes with distinct kinetochore size throughout mitosis. We show that centromere and kinetochore functional layers scale proportionally with centromere size. Measurement of intra-kinetochore distances, serial-section electron microscopy, and RNAi against key kinetochore proteins confirmed a standard structural and functional organization of the Indian muntjac kinetochores and revealed that microtubule binding capacity scales with kinetochore size. Surprisingly, we found that chromosome segregation in this species is not random. Chromosomes with larger kinetochores bi-oriented more efficiently and showed a 2-fold bias to congress to the equator in a motor-independent manner. Despite robust correction mechanisms during unperturbed mitosis, chromosomes with larger kinetochores were also strongly biased to establish erroneous merotelic attachments and missegregate during anaphase. This bias was impervious to the experimental attenuation of polar ejection forces on chromosome arms by RNAi against the chromokinesin Kif4a. Thus, kinetochore size is an important determinant of chromosome segregation fidelity
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