6,689 research outputs found
Superconducting magnesium diboride films on Silicon with Tc0 about 24K grown via vacuum annealing from stoichiometric precursors
Superconducting magnesium diboride films with Tc0 ~ 24 K and sharp transition
\~ 1 K were successfully prepared on silicon substrates by pulsed laser
deposition from a stoichiometric MgB2 target. Contrary to previous reports,
anneals at 630 degree and a background of 2x10^(-4) torr Ar/4%H2 were performed
without the requirement of Mg vapor or an Mg cap layer. This integration of
superconducting MgB2 films on silicon may thus prove enabling in
superconductor-semiconductor device applications. Images of surface morphology
and cross-section profiles by scanning electron microscopy (SEM) show that the
films have a uniform surface morphology and thickness. Energy dispersive
spectroscopy (EDS) reveals these films were contaminated with oxygen,
originating either from the growth environment or from sample exposure to air.
The oxygen contamination may account for the low Tc for those in-situ annealed
films, while the use of Si as the substrate does not result in a decrease in Tc
as compared to other substrates.Comment: 5 pages, 4 figures, 15 references; due to file size limit, images
were blure
Drought events and their effects on vegetation productivity in China
Many parts of the world have experienced frequent and severe droughts during the last few decades. Most previous studies examined the effects of specific drought events on vegetation productivity. In this study, we characterized the drought events in China from 1982 to 2012 and assessed their effects on vegetation productivity inferred from satellite data. We first assessed the occurrence, spatial extent, frequency, and severity of drought using the Palmer Drought Severity Index (PDSI). We then examined the impacts of droughts on China\u27s terrestrial ecosystems using the Normalized Difference Vegetation Index (NDVI). During the period 1982–2012, China\u27s land area (%) experiencing drought showed an insignificant trend. However, the drought conditions had been more severe over most regions in northern parts of China since the end of the 1990s, indicating that droughts hit these regions more frequently due to the drier climate. The severe droughts substantially reduced annual and seasonal NDVI. The magnitude and direction of the detrended NDVI under drought stress varied with season and vegetation type. The inconsistency between the regional means of PDSI and detrended NDVI could be attributed to different responses of vegetation to drought and the timing, duration, severity, and lag effects of droughts. The negative effects of droughts on vegetation productivity were partly offset by the enhancement of plant growth resulting from factors such as lower cloudiness, warming climate, and human activities (e.g., afforestation, improved agricultural management practices)
On the error term in Weyl's law for the Heisenberg manifolds (II)
In this paper we study the mean square of the error term in the Weyl's law of
an irrational -dimensional Heisenberg manifold . An asymptotic formula
is established
Design and validation of a virtual player for studying interpersonal coordination in the mirror game
This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.The mirror game has been recently proposed as
a simple, yet powerful paradigm for studying interpersonal
interactions. It has been suggested that a virtual partner able
to play the game with human subjects can be an effective tool
to affect the underlying neural processes needed to establish the
necessary connections between the players, and also to provide
new clinical interventions for rehabilitation of patients suffering
from social disorders. Inspired by the motor processes of the
central nervous system (CNS) and the musculoskeletal system in
the human body, in this paper we develop a novel interactive
cognitive architecture based on nonlinear control theory to drive
a virtual player (VP) to play the mirror game with a human
player (HP) in different configurations. Specifically, we consider
two cases: the former where the VP acts as leader and the latter
where it acts as follower. The crucial problem is to design a
feedback control architecture capable of imitating and following
or leading a human player in a joint action task. Movement of
the end-effector of the VP is modeled by means of a feedback
controlled Haken-Kelso-Bunz (HKB) oscillator, which is coupled
with the observed motion of the HP measured in real time.
To this aim, two types of control algorithms (adaptive control
and optimal control) are used and implemented on the HKB
model so that the VP can generate a human-like motion while
satisfying certain kinematic constraints. A proof of convergence
of the control algorithms is presented in the paper together
with an extensive numerical and experimental validation of their
effectiveness. A comparison with other existing designs is also
discussed, showing the flexibility and the advantages of our
control-based approach.This work was funded by the European Project AlterEgo
FP7 ICT 2.9 - Cognitive Sciences and Robotics, Grant Number
600610
Packetization schemes for forward error correction in Internet video streaming
In this work, our focus is on video streaming applications with relatively strict delay constraints; for such applications, forward error correction (FEC) is the preferred channel coding technique to recover from packet losses. Moreover, since video packets are usually of different importance, optimal bit allocation across video packets results in different packets receiving unequal error protection (UEP)
The Transporter Classification Database: recent advances
The Transporter Classification Database (TCDB), freely accessible at http://www.tcdb.org, is a relational database containing sequence, structural, functional and evolutionary information about transport systems from a variety of living organisms, based on the International Union of Biochemistry and Molecular Biology-approved transporter classification (TC) system. It is a curated repository for factual information compiled largely from published references. It uses a functional/phylogenetic system of classification, and currently encompasses about 5000 representative transporters and putative transporters in more than 500 families. We here describe novel software designed to support and extend the usefulness of TCDB. Our recent efforts render it more user friendly, incorporate machine learning to input novel data in a semiautomatic fashion, and allow analyses that are more accurate and less time consuming. The availability of these tools has resulted in recognition of distant phylogenetic relationships and tremendous expansion of the information available to TCDB users
Kaluza-Klein Pistons with non-Commutative Extra Dimensions
We calculate the scalar Casimir energy and Casimir force for a
Kaluza-Klein piston setup in which the extra dimensional space contains a
non-commutative 2-sphere, . The cases to be studied are and respectively as extra dimensional spaces, with the
dimensional commutative torus. The validity of the results and the
regularization that the piston setup offers are examined in both cases. Finally
we examine the 1-loop corrected Casimir energy for one piston chamber, due to
the self interacting scalar field in the non-commutative geometry. The
computation is done within some approximations. We compare this case for the
same calculation done in Minkowski spacetime . A discussion on the
stabilization of the extra dimensional space within the piston setup follows at
the end of the article.Comment: 22 page
Towards a Better Understanding of the Relationship between Probabilistic Models in IR
Probability of relevance (PR) models are generally assumed to implement the Probability Ranking Principle (PRP) of IR, and recent publications claim that PR models and language models are similar. However, a careful analysis reveals two gaps in the chain of reasoning behind this statement. First, the PRP considers the relevance of particular documents, whereas PR models consider the relevance of any query-document pair. Second, unlike PR models, language models consider draws of terms and documents. We bridge the first gap by showing how the probability measure of PR models can be used to define the probabilistic model of the PRP. Furthermore, we argue that given the differences between PR models and language models, the second gap cannot be bridged at the probabilistic model level. We instead define a new PR model based on logistic regression, which has a similar score function to the one of the query likelihood model. The performance of both models is strongly correlated, hence providing a bridge for the second gap at the functional and ranking level. Understanding language models in relation with logistic regression models opens ample new research directions which we propose as future work
Non-linear microwave impedance of short and long Josephson Junctions
The non-linear dependence on applied field () or current () of the microwave (ac) impedance of both
short and long Josephson junctions is calculated under a variety of excitation
conditions. The dependence on the junction width is studied, for both field
symmetric (current anti-symmetric) and field anti-symmetric (current symmetric)
excitation configurations.The resistance shows step-like features every time a
fluxon (soliton) enters the junction, with a corresponding phase slip seen in
the reactance. For finite widths the interference of fluxons leads to some
interesting effects which are described. Many of these calculated results are
observed in microwave impedance measurements on intrinsic and fabricated
Josephson junctions in the high temperature superconductors, and new effects
are suggested. When a field () or current () is applied,
interesting phase locking effects are observed in the ac impedance
. In particular an almost periodic dependence on the dc bias is
seen similar to that observed in microwave experiments at very low dc field
bias. These results are generic to all systems with a potential
in the overdamped limit and subjected to an ac drive.Comment: 7 pages, 11 figure
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