2,553 research outputs found
Fast Digital Convolutions using Bit-Shifts
An exact, one-to-one transform is presented that not only allows digital
circular convolutions, but is free from multiplications and quantisation errors
for transform lengths of arbitrary powers of two. The transform is analogous to
the Discrete Fourier Transform, with the canonical harmonics replaced by a set
of cyclic integers computed using only bit-shifts and additions modulo a prime
number. The prime number may be selected to occupy contemporary word sizes or
to be very large for cryptographic or data hiding applications. The transform
is an extension of the Rader Transforms via Carmichael's Theorem. These
properties allow for exact convolutions that are impervious to numerical
overflow and to utilise Fast Fourier Transform algorithms.Comment: 4 pages, 2 figures, submitted to IEEE Signal Processing Letter
AdSplit: Separating smartphone advertising from applications
A wide variety of smartphone applications today rely on third-party
advertising services, which provide libraries that are linked into the hosting
application. This situation is undesirable for both the application author and
the advertiser. Advertising libraries require additional permissions, resulting
in additional permission requests to users. Likewise, a malicious application
could simulate the behavior of the advertising library, forging the user's
interaction and effectively stealing money from the advertiser. This paper
describes AdSplit, where we extended Android to allow an application and its
advertising to run as separate processes, under separate user-ids, eliminating
the need for applications to request permissions on behalf of their advertising
libraries.
We also leverage mechanisms from Quire to allow the remote server to validate
the authenticity of client-side behavior. In this paper, we quantify the degree
of permission bloat caused by advertising, with a study of thousands of
downloaded apps. AdSplit automatically recompiles apps to extract their ad
services, and we measure minimal runtime overhead. We also observe that most ad
libraries just embed an HTML widget within and describe how AdSplit can be
designed with this in mind to avoid any need for ads to have native code
Fast Mojette Transform for Discrete Tomography
A new algorithm for reconstructing a two dimensional object from a set of one
dimensional projected views is presented that is both computationally exact and
experimentally practical. The algorithm has a computational complexity of O(n
log2 n) with n = N^2 for an NxN image, is robust in the presence of noise and
produces no artefacts in the reconstruction process, as is the case with
conventional tomographic methods. The reconstruction process is approximation
free because the object is assumed to be discrete and utilizes fully discrete
Radon transforms. Noise in the projection data can be suppressed further by
introducing redundancy in the reconstruction. The number of projections
required for exact reconstruction and the response to noise can be controlled
without comprising the digital nature of the algorithm. The digital projections
are those of the Mojette Transform, a form of discrete linogram. A simple
analytical mapping is developed that compacts these projections exactly into
symmetric periodic slices within the Discrete Fourier Transform. A new digital
angle set is constructed that allows the periodic slices to completely fill all
of the objects Discrete Fourier space. Techniques are proposed to acquire these
digital projections experimentally to enable fast and robust two dimensional
reconstructions.Comment: 22 pages, 13 figures, Submitted to Elsevier Signal Processin
Quire: Lightweight Provenance for Smart Phone Operating Systems
Smartphone apps often run with full privileges to access the network and
sensitive local resources, making it difficult for remote systems to have any
trust in the provenance of network connections they receive. Even within the
phone, different apps with different privileges can communicate with one
another, allowing one app to trick another into improperly exercising its
privileges (a Confused Deputy attack). In Quire, we engineered two new security
mechanisms into Android to address these issues. First, we track the call chain
of IPCs, allowing an app the choice of operating with the diminished privileges
of its callers or to act explicitly on its own behalf. Second, a lightweight
signature scheme allows any app to create a signed statement that can be
verified anywhere inside the phone. Both of these mechanisms are reflected in
network RPCs, allowing remote systems visibility into the state of the phone
when an RPC is made. We demonstrate the usefulness of Quire with two example
applications. We built an advertising service, running distinctly from the app
which wants to display ads, which can validate clicks passed to it from its
host. We also built a payment service, allowing an app to issue a request which
the payment service validates with the user. An app cannot not forge a payment
request by directly connecting to the remote server, nor can the local payment
service tamper with the request
Economic Analysis of Impact Assessment of Production Technology of Paddy Cultivation in Nasik Region of Maharashtra in India
The study had assessed the impact assessment of production technology of paddy cultivation in Nasik region of Maharashtra for the year 2016-17, based on the data of costs and returns. Analytical techniques like benefit-cost ratio (BCR), technology adoption index, yield gap, were exercised to have the extent of economic impact of improved paddy technology. High adopter group earned the net profit of ` 2298.09/ha (BCR=1.32) compared to ` 3629.3/ha ( BCR= 1.06) for low adopter group. Average technology adoption index was 71.57 per cent indicating that the farmers adopting recommended production technology of paddy could get yield of 41.63q/ha. Factor share analysis showed that contribution of Char-sutri method to the total yield was the highest yield (i.e. 32.84 per cent) which was followed by urea (19.76 per cent), doses of manures (12.02 per cent), intercultural operation, planting distance, transplanting time contributes about 8.09 per cent etc. respectively. Estimates of yield gap analysis proved existence of yield gap in all level which ranged from 41 percent (low adopter) to 23 percent (high adopter). So, reduction or bridging up the yield gap may be utmost priority to increase the overall production and income of the farmers
People with Learning Disabilities and Smartphones: Testing the Usability of a Touch-Screen Interface
Mobile phone technology is becoming ubiquitous. However, a number of unique usability challenges are still unresolved, including small screen size, device orientation changes, and an array of interaction methods (tap, flick, pinch, etc.) These challenges may be particularly acute for people with learning disabilities. This study examined the usability of touchscreen interactions, the difficulties, and possible solutions. An app was developed in which (12) participants accessed Google Maps and manipulated it to find various London Underground station locations. Text input (a password), tap, swipe, and pinch were required, and their usage was analysed. Many participants were successful in finding the required information. However, many difficulties arose, including misunderstandings of the labelling (a live ‘Welcome’ button was not tapped, whereas a short list of instructions was erroneously seen as a menu and so erroneously tapped to access each step in the process) and an over-sensitive zoom feature. Three categories of error were formulated from the findings: affordance, user, and functionality. Recommendations are offered, such as using more appropriate ‘signage’ for link buttons (affordance); manipulating the zoom feature using + and - buttons rather than a ‘pinch’, which requires two fingered dexterity (functionality); and more formal training and familiarity (user)
Algorithms for Replica Placement in High-Availability Storage
A new model of causal failure is presented and used to solve a novel replica
placement problem in data centers. The model describes dependencies among
system components as a directed graph. A replica placement is defined as a
subset of vertices in such a graph. A criterion for optimizing replica
placements is formalized and explained. In this work, the optimization goal is
to avoid choosing placements in which a single failure event is likely to wipe
out multiple replicas. Using this criterion, a fast algorithm is given for the
scenario in which the dependency model is a tree. The main contribution of the
paper is an dynamic programming algorithm for placing
replicas on a tree with vertices. This algorithm exhibits the
interesting property that only two subproblems need to be recursively
considered at each stage. An greedy algorithm is also briefly
reported.Comment: 22 pages, 7 figures, 4 algorithm listing
Studies on Particle Suspension in Air-agitated Pachuca tanks
The paper presents the findings of an investigation involving extensive experiments on three laboratory scale Pachuca tanks to examine the effect of design and oper-ating parameters, as well as scale up on particle suspension. Some important results, crucial to the design and scale up have emerged. Full center column (FCC) Pachucas with a draft tube to tank diameter ratio (Dd/Dt) on the order of 0.1 are found to be energetically more efficient in suspending particles than Free-Air.Lift (FAL) and Stub Column (SC) Pachuca tanks. It has been established
that the energy required for generating suspension from settled particles is more than that is required for maintaining the particles already in suspension. The magn-itude of hysterisis in FCC Pachuca tanks is of the order of 20%. Effect of novel split air injection technique on critical velocity for particle suspension has been rigorously investigated. Split air injection, with 30% air injected into the annulus from top and 70% air injected from the bottom into the draft tube lowers the critical air
velocity for particle suspension by about 37% with respect to bottom blown Pachuca tanks. Mechanisms for particle suspension in bottom blow Pachucas as well as those with split air injection are proposed
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