29,437 research outputs found
Do Stated Preference Values Predict Revealed Behavior in “New” Markets for Ecosystem Services? A Comparison of Experiments Addressing Establishing A Market for Farmland Ecosystem Services
Resource /Energy Economics and Policy,
Android Malware Clustering through Malicious Payload Mining
Clustering has been well studied for desktop malware analysis as an effective
triage method. Conventional similarity-based clustering techniques, however,
cannot be immediately applied to Android malware analysis due to the excessive
use of third-party libraries in Android application development and the
widespread use of repackaging in malware development. We design and implement
an Android malware clustering system through iterative mining of malicious
payload and checking whether malware samples share the same version of
malicious payload. Our system utilizes a hierarchical clustering technique and
an efficient bit-vector format to represent Android apps. Experimental results
demonstrate that our clustering approach achieves precision of 0.90 and recall
of 0.75 for Android Genome malware dataset, and average precision of 0.98 and
recall of 0.96 with respect to manually verified ground-truth.Comment: Proceedings of the 20th International Symposium on Research in
Attacks, Intrusions and Defenses (RAID 2017
Cold atoms in non-Abelian gauge potentials: From the Hofstadter "moth" to lattice gauge theory
We demonstrate how to create artificial external non-Abelian gauge potentials
acting on cold atoms in optical lattices. The method employs internal
states of atoms and laser assisted state sensitive tunneling. Thus, dynamics
are communicated by unitary -matrices. By experimental control of
the tunneling parameters, the system can be made truly non-Abelian. We show
that single particle dynamics in the case of intense U(2) vector potentials
lead to a generalized Hofstadter butterfly spectrum which shows a complex
``moth''-like structure. We discuss the possibility to employ non-Abelian
interferometry (Aharonov-Bohm effect) and address methods to realize matter
dynamics in specific classes of lattice gauge fields.Comment: 5 pages, 3 figure
Regionalização espacial do nordeste do Estado do Pará.
bitstream/item/40416/1/Boletim-Pesquisa-15-CPATU.pd
Primary beam effects of radio astronomy antennas -- II. Modelling the MeerKAT L-band beam
After a decade of design and construction, South Africa's SKA-MID precursor
MeerKAT has begun its science operations. To make full use of the widefield
capability of the array, it is imperative that we have an accurate model of the
primary beam of its antennas. We have taken available L-band full-polarization
'astro-holographic' observations of three antennas and a generic
electromagnetic simulation and created sparse representations of the beams
using principal components and Zernike polynomials. The spectral behaviour of
the spatial coefficients has been modelled using discrete cosine transform. We
have provided the Zernike-based model over a diameter of 10 deg averaged over
the beams of three antennas in an associated software tool (EIDOS) that can be
useful in direction-dependent calibration and imaging. The model is more
accurate for the diagonal elements of the beam Jones matrix and at lower
frequencies. As we get more accurate beam measurements and simulations in the
future, especially for the cross-polarization patterns, our pipeline can be
used to create more accurate sparse representations of MeerKAT beams.Comment: 16 pages, 18 figures. This is a pre-copyedited, author-produced PDF
of an article accepted for publication in MNRAS following peer review. The
version of record [K. M. B. Asad et al., 2021] is available online at:
https://doi.org/10.1093/mnras/stab10
Total And Segmental Colonic Transit Time In Constipated Patients With Chagas' Disease Without Megaesophagus Or Megacolon.
Manometric and pharmacological tests have shown that motor abnormalities may occur in the non-dilated colons of chagasic patients. In order to investigate the presence of abnormalities of colonic function in constipated patients with Chagas' disease (ChC) without megaesophagus or megacolon, studies of total and segmental colonic transit time with radiopaque markers were performed on 15 ChC patients, 27 healthy volunteers and 17 patients with idiopathic constipation (IC). The values obtained for the control group were similar to those reported in the literature (total colonic time: 34. 1 +/- 15.6 h; right colon: 9.9 +/- 7.3 h; left colon: 10.8 +/- 10 h, and rectosigmoid: 12.6 +/- 9.9 h). Colonic transit time data permitted us to divide both IC and ChC patients into groups with normal transit and those with slow colonic transit. Colonic inertia was detected in 41% of IC patients and in 13% of ChC patients; left colon isolated stasis (hindgut dysfunction) was detected in 12% of IC patients and 7% of ChC patients, and outlet obstruction was detected in 6% of IC patients and 7% of ChC patients. There were no significant differences in total or segmental colonic transit times between slow transit IC and slow transit ChC patients. In conclusion, an impairment of colonic motility was detected in about 30% of constipated patients with Chagas' disease without megaesophagus or megacolon. This subgroup of patients presented no distinctive clinical feature or pattern of colonic dysmotility when compared to patients with slow transit idiopathic constipation.3343-
Probing the quantum phase transition in the Dicke model through mechanical vibrations
This paper is concerned with quantum dynamics of a system coupled to a
critical reservoir. In this context, we employ the Dicke model which is known
to exhibit a super radiant quantum phase transition (QPT) and we allow one of
the mirrors to move under a linear restoring force. The electromagnetic field
couples to the movable mirror though radiation pressure just like in typical
optomechanical setups. We show that, in the thermodynamical limit, the
super-radiant phase induces a classical driving force on the mirror without
causing decoherence.Comment: 6 pages, 3 figures, final versio
Design of nano- and microfiber combined scaffolds by electrospinning of collagen onto starch-based fiber meshes : a man-made equivalent of natural extracellular matrix
Mimicking the structural organization and biologic function of natural extracellular matrix has been one of the
main goals of tissue engineering. Nevertheless, the majority of scaffolding materials for bone regeneration
highlights biochemical functionality in detriment of mechanical properties. In this work we present a rather
innovative construct that combines in the same structure electrospun type I collagen nanofibers with starchbased
microfibers. These combined structures were obtained by a two-step methodology and structurally consist
in a type I collagen nano-network incorporated on a macro starch-based support. The morphology of the
developed structures was assessed by several microscopy techniques and the collagenous nature of the nanonetwork
was confirmed by immunohistochemistry. In addition, and especially regarding the requirements of
large bone defects, we also successfully introduced the concept of layer by layer, as a way to produce thicker
structures. In an attempt to recreate bone microenvironment, the design and biochemical composition of the
combined structures also envisioned bone-forming cells and endothelial cells (ECs). The inclusion of a type I
collagen nano-network induced a stretched morphology and improved the metabolic activity of osteoblasts.
Regarding ECs, the presence of type I collagen on the combined structures provided adhesive support and
obviated the need of precoating with fibronectin. It was also importantly observed that ECs on the nano-network
organized into circular structures, a three-dimensional arrangement distinct from that observed for osteoblasts
and resembling the microcappillary-like organizations formed during angiogenesis. By providing simultaneously
physical and chemical cues for cells, the herein-proposed combined structures hold a great potential in
bone regeneration as a man-made equivalent of extracellular matrixK. Tuzlakoglu and M. I. Santos thank the Portuguese Foundation for Science and Technology for their Ph.D. scholarship (SFRH/BD/8502/2002 and SFRH/BD/13428/2003). This work was partially supported by FCT Foundation for Science and Technology, through funds from the POCTI and/or FEDER programs and by the European Union funded STREP Project HIPPOCRATES (NMP3-CT-2003-505758). This work was carried out under the scope of the European NoE EXPERTISSUES (NMP3-CT-2004-500283). Work developed under the cooperation agreement between UM-3B's research group and the Hospital de S. Marcos, Braga. The authors thank to L. Goreti Pinto for her help on confocal microscopy studies
Dynamical Cooling of Trapped Gases I: One Atom Problem
We study the laser cooling of one atom in an harmonic trap beyond the
Lamb-Dicke regime. By using sequences of laser pulses of different detunings we
show that the atom can be confined into just one state of the trap, either the
ground state or an excited state of the harmonic potential. The last can be
achieved because under certain conditions an excited state becomes a dark
state. We study the problem in one and two dimensions. For the latter case a
new cooling mechanism is possible, based on the destructive interference
between the effects of laser fields in different directions, which allows the
creation of variety of dark states. For both, one and two dimensional cases,
Monte Carlo simulations of the cooling dynamics are presented.Comment: LaTeX file with 8 pages, 7 eps figures. Submitted to Phys. Rev.
Continuous optical loading of a Bose-Einstein Condensate
The continuous pumping of atoms into a Bose-Einstein condensate via
spontaneous emission from a thermal reservoir is analyzed. We consider the case
of atoms with a three-level scheme, in which one of the atomic
transitions has a very much shorter life-time than the other one. We found that
in such scenario the photon reabsorption in dense clouds can be considered
negligible. If in addition inelastic processes can be neglected, we find that
optical pumping can be used to continuously load and refill Bose-Einstein
condensates, i.e. provides a possible way to achieve a continuous atom laser.Comment: 12 pages, 8 figure
- …