9,439 research outputs found
Supporting disconnected operations in mobile computing
Mobile computing has enabled users to seamlessly access databases even when they are on the move. However, in the absence of readily available high-quality communication, users are often forced to operate disconnected from the network. As a result, software applications have to be redesigned to take advantage of this environment while accommodating the new challenges posed by mobility. In particular, there is a need for replication and synchronization services in order to guarantee availability of data and functionality, (including updates) in disconnected mode. To this end we propose a scalable and highly available data replication and management service. The proposed replication technique is compared with a baseline replication technique and shown to exhibit high availability, fault tolerance and minimal access times of the data and services, which are very important in an environment with low-quality communication links.<br /
Open strings with topologically inspired boundary conditions
We consider an open string described by an action of the Dirac-Nambu-Goto
type with topological corrections which affect the boundary conditions but not
the equations of motion. The most general addition of this kind is a sum of the
Gauss-Bonnet action and the first Chern number (when the background spacetime
dimension is four) of the normal bundle to the string worldsheet. We examine
the modification introduced by such terms in the boundary conditions at the
ends of the string.Comment: 12 pages, late
Managing Inventory: A Study of Databases and Database Management Systems
Databases play an important role in the storage and manipulation of data. Databases and database management systems allow for fast and efficient data querying that has recently become increasingly important in most companies and organizations. This paper introduces a few of the different types of database management systems that are in widespread use today. It introduces some important terminology related to databases and database management systems. This paper also briefly discusses web user interfaces, highlighting important user interface design principles. Finally, an inventory management system is implemented for a local stationery store and is integrated with a web application to serve as the front end
The classification of a Sesbania sesban (sssesban) collection. II. Agronomic attributes and their relation to biomass estimation
A collection of Sesbania sesban accessions was grown out in the field and classified using real and standardised values of 10 agronomic attributes. Clustering the accessions using the observed values of the attributes produced several groups which were mainly based on the dry matter yields after the first and second harvests. The cluster analysis on the standardised values of the descriptors provided 10 similarity groups. These groups were identified and compared with an earlier morphological classification. Some of the observed characters were used to establish their relationship with biomass yield of the trees. The data were therefore subjected to linear regression analysis. Predictive equations were obtained for the logarithmical transformed biomass yield using stem diameter at 30 cm from ground level plus the plant height with r to the square root of 2 values between 84 and 89 percent
Force dipoles and stable local defects on fluid vesicles
An exact description is provided of an almost spherical fluid vesicle with a
fixed area and a fixed enclosed volume locally deformed by external normal
forces bringing two nearby points on the surface together symmetrically. The
conformal invariance of the two-dimensional bending energy is used to identify
the distribution of energy as well as the stress established in the vesicle.
While these states are local minima of the energy, this energy is degenerate;
there is a zero mode in the energy fluctuation spectrum, associated with area
and volume preserving conformal transformations, which breaks the symmetry
between the two points. The volume constraint fixes the distance , measured
along the surface, between the two points; if it is relaxed, a second zero mode
appears, reflecting the independence of the energy on ; in the absence of
this constraint a pathway opens for the membrane to slip out of the defect.
Logarithmic curvature singularities in the surface geometry at the points of
contact signal the presence of external forces. The magnitude of these forces
varies inversely with and so diverges as the points merge; the
corresponding torques vanish in these defects. The geometry behaves near each
of the singularities as a biharmonic monopole, in the region between them as a
surface of constant mean curvature, and in distant regions as a biharmonic
quadrupole. Comparison of the distribution of stress with the quadratic
approximation in the height functions points to shortcomings of the latter
representation. Radial tension is accompanied by lateral compression, both near
the singularities and far away, with a crossover from tension to compression
occurring in the region between them.Comment: 26 pages, 10 figure
Contact lines for fluid surface adhesion
When a fluid surface adheres to a substrate, the location of the contact line
adjusts in order to minimize the overall energy. This adhesion balance implies
boundary conditions which depend on the characteristic surface deformation
energies. We develop a general geometrical framework within which these
conditions can be systematically derived. We treat both adhesion to a rigid
substrate as well as adhesion between two fluid surfaces, and illustrate our
general results for several important Hamiltonians involving both curvature and
curvature gradients. Some of these have previously been studied using very
different techniques, others are to our knowledge new. What becomes clear in
our approach is that, except for capillary phenomena, these boundary conditions
are not the manifestation of a local force balance, even if the concept of
surface stress is properly generalized. Hamiltonians containing higher order
surface derivatives are not just sensitive to boundary translations but also
notice changes in slope or even curvature. Both the necessity and the
functional form of the corresponding additional contributions follow readily
from our treatment.Comment: 8 pages, 2 figures, LaTeX, RevTeX styl
Conical defects in growing sheets
A growing or shrinking disc will adopt a conical shape, its intrinsic
geometry characterized by a surplus angle at the apex. If growth is slow,
the cone will find its equilibrium. Whereas this is trivial if , the
disc can fold into one of a discrete infinite number of states if is
positive. We construct these states in the regime where bending dominates,
determine their energies and how stress is distributed in them. For each state
a critical value of is identified beyond which the cone touches itself.
Before this occurs, all states are stable; the ground state has two-fold
symmetry.Comment: 4 pages, 4 figures, LaTeX, RevTeX style. New version corresponds to
the one published in PR
Deformations of extended objects with edges
We present a manifestly gauge covariant description of fluctuations of a
relativistic extended object described by the Dirac-Nambu-Goto action with
Dirac-Nambu-Goto loaded edges about a given classical solution. Whereas
physical fluctuations of the bulk lie normal to its worldsheet, those on the
edge possess an additional component directed into the bulk. These fluctuations
couple in a non-trivial way involving the underlying geometrical structures
associated with the worldsheet of the object and of its edge. We illustrate the
formalism using as an example a string with massive point particles attached to
its ends.Comment: 17 pages, revtex, to appear in Phys. Rev. D5
Covariant perturbations of domain walls in curved spacetime
A manifestly covariant equation is derived to describe the perturbations in a
domain wall on a given background spacetime. This generalizes recent work on
domain walls in Minkowski space and introduces a framework for examining the
stability of relativistic bubbles in curved spacetimes.Comment: 15 pages,ICN-UNAM-93-0
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