7,914 research outputs found
Global Monopole in Asymptotically dS/AdS Spacetime
In this paper, we investigate the global monopole in asymptotically dS/Ads
spacetime and find that the mass of the monopole in the asymptotically dS
spacetime could be positive if the cosmological constant is greater than a
critical value. This shows that the gravitational field of the global monopole
could be attractive or repulsive depending on the value of the cosmological
constant.Comment: 5 pages, 1 figure, to appear in Phys. Rev.
Knowledge Construction by Users: A Content Analysis Framework and A Knowledge Construction Process Model for Virtual Product User Communities
Purpose–The purpose of this study is to develop a content analysis framework and from
that derive a process model of knowledge construction in the context of virtual product user
communities, organization sponsored online forums where product users collaboratively
construct knowledge to solve their technical problems.
Design/methodology/approach–The study is based on a deductive, qualitative content
analysis of discussion threads about solving technical problems selected from a series of
virtual product user communities. This data is complemented with thematic analysis of
interviews with forum members.
Findings–This research develops a content analysis framework for knowledge construction.
It is based on a combination of existing codes derived from frameworks developed for
Computer Supported Collaborative Learning (CSCL) and new categories identified from the
data. Analysis using this framework allows the authors to propose a knowledge construction
process model showing how these elements are organised around a typical “trial-and-error”
knowledge construction strategy.
Practical Implications–The research makes suggestions about organizations’ management
of knowledge activities in virtual product user communities, including moderators’ roles in
facilitation.
Originality/Value– The paper outlines a new framework for analysing knowledge activities
where there is a low level of critical thinking and a model of knowledge construction by trial
and error. The new framework and model can be applied in other similar contexts
Investigating the impact of combining handwritten signature and keyboard keystroke dynamics for gender prediction
© 2019 IEEE. The use of soft-biometric data as an auxiliary tool on user identification is already well known. Gender, handorientation and emotional state are some examples which can be called soft-biometrics. These soft-biometric data can be predicted directly from the biometric templates. It is very common to find researches using physiological modalities for soft-biometric prediction, but behavioural biometric is often not well explored for this context. Among the behavioural biometric modalities, keystroke dynamics and handwriting signature have been widely explored for user identification, including some soft-biometric predictions. However, in these modalities, the soft-biometric prediction is usually done in an individual way. In order to fill this space, this study aims to investigate whether the combination of those two biometric modalities can impact the performance of a soft-biometric data, gender prediction. The main aim is to assess the impact of combining data from two different biometric sources in gender prediction. Our findings indicated gains in terms of performance for gender prediction when combining these two biometric modalities, when compared to the individual ones
Do phytoplankton nutrient ratios reflect patterns of water column nutrient ratios? A numerical stoichiometric analysis of Lake Kinneret
AbstractThe N:P stoichiometry of a water body is one of the most commonly used indicators of its nutrient status. However, in a dynamic aquatic ecosystem the N:P stoichiometry of phytoplankton is highly variable depending on a range of factors that influence their growth. In this study, a 1D hydrodynamic-ecological model was used to examine how the internal nutrient ratios of phytoplankton relate to nutrient ratios within the water column in Lake Kinneret, Israel. We identified that seasonal patterns of the simulated dissolved inorganic N to total P (DIN:TP) ratios in the water column were a useful indicator of the N:P stoichiometry of the combined phytoplankton community. However, the internal N:P patterns of individual phytoplankton groups did not necessarily relate to DIN:TP patterns
A mechanism to derive multi-power law functions: an application in the econophysics framework
It is generally recognized that economical systems, and more in general
complex systems, are characterized by power law distributions. Sometime, these
distributions show a changing of the slope in the tail so that, more
appropriately, they show a multi-power law behavior. We present a method to
derive analytically a two-power law distribution starting from a single power
law function recently obtained, in the frameworks of the generalized
statistical mechanics based on the Sharma-Taneja-Mittal information measure. In
order to test the method, we fit the cumulative distribution of personal income
and gross domestic production of several countries, obtaining a good agreement
for a wide range of data.Comment: 10pages, 3 figures. Presented at Int. Conf. on Application of Physics
in Financial Analisys (APFA5), June 29 - July 1, 2006 Torino, Ital
Uranium on uranium collisions at relativistic energies
Deformation and orientation effects on compression, elliptic flow and
particle production in uranium on uranium collisions (UU) at relativistic
energies are studied within the transport model ART. The density compression in
tip-tip UU collisions is found to be about 30% higher and lasts approximately
50% longer than in body-body or spherical UU reactions. The body-body UU
collisions have the unique feature that the nucleon elliptic flow is the
highest in the most central collisions and remain a constant throughout the
reaction. We point out that the tip-tip UU collisions are more probable to
create the QGP at AGS and SPS energies while the body-body UU collisions are
more useful for studying properties of the QGP at higher energies.Comment: 8 pages + 4 figure
Negative c-axis magnetoresistance in graphite
We have studied the c-axis interlayer magnetoresistance (ILMR), R_c(B) in
graphite. The measurements have been performed on strongly anisotropic highly
oriented pyrolytic graphite (HOPG) samples in magnetic field up to B = 9 T
applied both parallel and perpendicular to the sample c-axis in the temperature
interval 2 K < T < 300 K. We have observed negative magnetoresistance, dR_c/dB
< 0, for B || c-axis above a certain field B_m(T) that reaches its minimum
value B_m = 5.4 T at T = 150 K. The results can be consistently understood
assuming that ILMR is related to a tunneling between zero-energy Landau levels
of quasi-two-dimensional Dirac fermions, in a close analogy with the behavior
reported for alpha-(BEDT-TTF)2I3 [N. Tajima et al., Phys. Rev. Lett. 102,
176403 (2009)], another multilayer Dirac electron system.Comment: 14 pages, including 4 figure
Priority-based initial access for URLLC traffic in massive IoT networks: Schemes and performance analysis
At a density of one million devices per square kilometer, the10’s of billions of devices, objects, and machines
that form a massive Internet of things (mIoT) require ubiquitous connectivity. Among a massive number of
IoT devices, a portion of them require ultra-reliable low latency communication (URLLC) provided via fifth
generation (5G) networks, bringing many new challenges due to the stringent service requirements. Albeit a surge
of research efforts on URLLC and mIoT, access mechanisms which include both URLLC and massive machine
type communications (mMTC) have not yet been investigated in-depth. In this paper, we propose three novel
schemes to facilitate priority-based initial access for mIoT/mMTC devices that require URLLC services while also
considering the requirements of other mIoT/mMTC devices. Based on a long term evolution-advanced (LTEA) or 5G new radio frame structure, the proposed schemes enable device grouping based on device vicinity
or/and their URLLC requirements and allocate dedicated preambles for grouped devices supported by flexible
slot allocation for random access. These schemes are able not only to increase the reliability and minimize the
delay of URLLC devices but also to improve the performance of all involved mIoT devices. Furthermore, we
evaluate the performance of the proposed schemes through mathematical analysis as well as simulations and
compare the results with the performance of both the legacy LTE-A based initial access scheme and a grant-free
transmission scheme.acceptedVersio
Larmor precession and tunneling time of a relativistic neutral spinning particle through an arbitrary potential barrier
The Larmor precession of a relativistic neutral spin-1/2 particle in a
uniform constant magnetic field confined to the region of a one-dimensional
arbitrary potential barrier is investigated. The spin precession serves as a
clock to measure the time spent by a quantum particle traversing a potential
barrier. With the help of general spin coherent state it is explicitly shown
that the precession time is equal to the dwell time.Comment: 10 pages, 1 figure. To be published in Phys. Rev. A (01 February
2002
Modal decomposition of a propagating matter wave via electron ptychography
We employ ptychography, a phase-retrieval imaging technique, to show experimentally for the first
time that a partially coherent high-energy matter (electron) wave emanating from an extended source
can be decomposed into a set of mutually independent modes of minimal rank. Partial coherence
significantly determines the optical transfer properties of an electron microscope and so there has
been much work on this subject. However, previous studies have employed forms of interferometry to
determine spatial coherence between discrete points in the wavefield. Here we use the density matrix
to derive a formal quantum mechanical description of electron ptychography and use it to measure a
full description of the spatial coherence of a propagating matter wavefield, at least to the within the
fundamental uncertainties of the measurements we can obtain
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