2,757 research outputs found
Coherent Quantum Ratchets Driven by Tunnel Oscillations
We demonstrate that the tunnel oscillations of a biased double quantum dot
can be employed as driving source for a quantum ratchet. As a model, we use two
capacitively coupled double quantum dots. One double dot is voltage biased and
provides the ac force, while the other experiences the ac force and acts as
coherent quantum ratchet. The current is obtained from a Bloch-Redfield master
equation which ensures a proper equilibrium limit. We find that the
two-electron states of the coupled ratchet-drive Hamiltonian lead to unexpected
steps in the ratchet current.Comment: 4 pages, 4 figure
Do Phillips curves conditionally help to forecast inflation?
The Phillips curve has long been used as a foundation for forecasting inflation. Yet numerous studies indicate that over the past 20 years or so, inflation forecasts based on the Phillips curve generally do not predict inflation any better than a univariate forecasting model. In this paper, the authors take a deeper look at the forecasting ability of Phillips curves from both an unconditional and a conditional view. Namely, they use the test results developed by Giacomini and White (2006) to examine the forecasting ability of Phillips curve models. The authors' main results indicate that forecasts from their Phillips curve models are unconditionally inferior to those of their univariate forecasting models and sometimes the difference is statistically significant. However, the authors do find that conditioning on various measures of the state of the economy does at times improve the performance of the Phillips curve model in a statistically significant way. Of interest is that improvement is more likely to occur at longer forecasting horizons and over the sample period 1984Q1â2010Q3. Strikingly, the improvement is asymmetric â Phillips curve forecasts tend to be more accurate when the economy is weak and less accurate when the economy is strong. It, therefore, appears that forecasters should not fully discount the inflation forecasts of Phillips curve-based models when the economy is weak.Phillips curve ; Unemployment
Multi-View Priors for Learning Detectors from Sparse Viewpoint Data
While the majority of today's object class models provide only 2D bounding
boxes, far richer output hypotheses are desirable including viewpoint,
fine-grained category, and 3D geometry estimate. However, models trained to
provide richer output require larger amounts of training data, preferably well
covering the relevant aspects such as viewpoint and fine-grained categories. In
this paper, we address this issue from the perspective of transfer learning,
and design an object class model that explicitly leverages correlations between
visual features. Specifically, our model represents prior distributions over
permissible multi-view detectors in a parametric way -- the priors are learned
once from training data of a source object class, and can later be used to
facilitate the learning of a detector for a target class. As we show in our
experiments, this transfer is not only beneficial for detectors based on
basic-level category representations, but also enables the robust learning of
detectors that represent classes at finer levels of granularity, where training
data is typically even scarcer and more unbalanced. As a result, we report
largely improved performance in simultaneous 2D object localization and
viewpoint estimation on a recent dataset of challenging street scenes.Comment: 13 pages, 7 figures, 4 tables, International Conference on Learning
Representations 201
Software Engineering Laboratory Ada performance study: Results and implications
The SEL is an organization sponsored by NASA/GSFC to investigate the effectiveness of software engineering technologies applied to the development of applications software. The SEL was created in 1977 and has three organizational members: NASA/GSFC, Systems Development Branch; The University of Maryland, Computer Sciences Department; and Computer Sciences Corporation, Systems Development Operation. The goals of the SEL are as follows: (1) to understand the software development process in the GSFC environments; (2) to measure the effect of various methodologies, tools, and models on this process; and (3) to identify and then to apply successful development practices. The activities, findings, and recommendations of the SEL are recorded in the Software Engineering Laboratory Series, a continuing series of reports that include the Ada Performance Study Report. This paper describes the background of Ada in the Flight Dynamics Division (FDD), the objectives and scope of the Ada Performance Study, the measurement approach used, the performance tests performed, the major test results, and the implications for future FDD Ada development efforts
Coordinate actions of BMPs, Wnts, Shh and noggin mediate patterning of the dorsal somite
Shortly after their formation, somites of vertebrate embryos
differentiate along the dorsoventral axis into sclerotome,
myotome and dermomyotome. The dermomyotome is then
patterned along its mediolateral axis into medial, central
and lateral compartments, which contain progenitors of
epaxial muscle, dermis and hypaxial muscle, respectively.
Here, we used Wnt-11 as a molecular marker for the medial
compartment of dermomyotome (the âmedial lipâ) to
demonstrate that BMP in the dorsal neural tube indirectly
induces formation of the medial lip by up-regulating Wnt-1
and Wnt-3a (but not Wnt-4) expression in the neural tube.
Noggin in the dorsal somite may inhibit the direct action of
BMP on this tissue. Wnt-11 induction is antagonized by
Sonic Hedgehog, secreted by the notochord and the floor
plate. Together, our results show that the coordinated
actions of the dorsal neural tube (via BMP and Wnts), the
ventral neural tube/notochord (via Shh) and the somite
itself (via noggin) mediates patterning of the dorsal compartment of the somite
Culture, Utility or Social Systems?:Explaining the Cross-National Ties of Emigrants from Borsa, Romania
Emigrants from BorĆa, Romania, display two quite distinct patterns of ties with their community of origin: migration to Italy is discernibly transnational, with a strong reliance on migrant networks; while migration to the UK is more individualistic, with emigrants shunning interaction with compatriots and retaining only weak ties to BorĆa. We argue that prevalent theories of cross-national ties fail adequately to explain this divergence. Instead, we draw on systems theory to explain the discrepancy in terms of divergent conditions for societal inclusion. In Italy, incorporation into parallel, unofficial structures of work, welfare and accommodation encouraged a reliance on cultural criteria for maintaining social ties. In the UK, migrants were obliged to integrate into state-sponsored systems, encouraging the relinquishing of ethnic ties in favour of more strategic networking to facilitate societal inclusion
3D Object Class Detection in the Wild
Object class detection has been a synonym for 2D bounding box localization
for the longest time, fueled by the success of powerful statistical learning
techniques, combined with robust image representations. Only recently, there
has been a growing interest in revisiting the promise of computer vision from
the early days: to precisely delineate the contents of a visual scene, object
by object, in 3D. In this paper, we draw from recent advances in object
detection and 2D-3D object lifting in order to design an object class detector
that is particularly tailored towards 3D object class detection. Our 3D object
class detection method consists of several stages gradually enriching the
object detection output with object viewpoint, keypoints and 3D shape
estimates. Following careful design, in each stage it constantly improves the
performance and achieves state-ofthe-art performance in simultaneous 2D
bounding box and viewpoint estimation on the challenging Pascal3D+ dataset
Neural tube-ectoderm interactions are required for trigeminal placode formation
Cranial sensory ganglia in vertebrates develop from the ectodermal placodes, the neural crest, or both. Although much is known about the neural crest contribution to cranial ganglia, relatively little is known about how placode cells form, invaginate and migrate to their targets. Here, we identify Pax-3 as a molecular marker for placode cells that contribute to the ophthalmic branch of the trigeminal ganglion and use it, in conjunction with DiI labeling of the surface ectoderm, to analyze some of the mechanisms underlying placode development. Pax-3 expression in the ophthalmic placode is observed as early as the 4-somite stage in a narrow band of ectoderm contiguous to the midbrain neural folds. Its expression broadens to a patch of ectoderm adjacent to the midbrain and the rostral hindbrain at the 8- to 10-somite stage. Invagination of the first Pax-3-positive cells begins at the 13-somite stage. Placodal invagination continues through the 35-somite stage, by which time condensation of the trigeminal ganglion has begun. To challenge the normal tissue interactions leading to placode formation, we ablated the cranial neural crest cells or implanted barriers between the neural tube and the ectoderm. Our results demonstrate that, although the presence of neural crest cells is not mandatory for Pax-3 expression in the forming placode, a diffusible signal from the neuroectoderm is required for induction and/or maintenance of the ophthalmic placode
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