5,391 research outputs found
Finding Cycles and Trees in Sublinear Time
We present sublinear-time (randomized) algorithms for finding simple cycles
of length at least and tree-minors in bounded-degree graphs. The
complexity of these algorithms is related to the distance of the graph from
being -minor-free (resp., free from having the corresponding tree-minor).
In particular, if the graph is far (i.e., -far) {from} being
cycle-free, i.e. if one has to delete a constant fraction of edges to make it
cycle-free, then the algorithm finds a cycle of polylogarithmic length in time
\tildeO(\sqrt{N}), where denotes the number of vertices. This time
complexity is optimal up to polylogarithmic factors.
The foregoing results are the outcome of our study of the complexity of {\em
one-sided error} property testing algorithms in the bounded-degree graphs
model. For example, we show that cycle-freeness of -vertex graphs can be
tested with one-sided error within time complexity
\tildeO(\poly(1/\e)\cdot\sqrt{N}). This matches the known
query lower bound, and contrasts with the fact that any minor-free property
admits a {\em two-sided error} tester of query complexity that only depends on
the proximity parameter \e. For any constant , we extend this result
to testing whether the input graph has a simple cycle of length at least .
On the other hand, for any fixed tree , we show that -minor-freeness has
a one-sided error tester of query complexity that only depends on the proximity
parameter \e.
Our algorithm for finding cycles in bounded-degree graphs extends to general
graphs, where distances are measured with respect to the actual number of
edges. Such an extension is not possible with respect to finding tree-minors in
complexity.Comment: Keywords: Sublinear-Time Algorithms, Property Testing, Bounded-Degree
Graphs, One-Sided vs Two-Sided Error Probability Updated versio
Some economic benefits of a synchronous earth observatory satellite
An analysis was made of the economic benefits which might be derived from reduced forecasting errors made possible by data obtained from a synchronous satellite system which can collect earth observation and meteorological data continuously and on demand. User costs directly associated with achieving benefits are included. In the analysis, benefits were evaluated which might be obtained as a result of improved thunderstorm forecasting, frost warning, and grain harvest forecasting capabilities. The anticipated system capabilities were used to arrive at realistic estimates of system performance on which to base the benefit analysis. Emphasis was placed on the benefits which result from system forecasting accuracies. Benefits from improved thunderstorm forecasts are indicated for the construction, air transportation, and agricultural industries. The effects of improved frost warning capability on the citrus crop are determined. The benefits from improved grain forecasting capability are evaluated in terms of both U.S. benefits resulting from domestic grain distribution and U.S. benefits from international grain distribution
Top Quark and Higgs Boson Masses: Interplay between Infrared and Ultraviolet Physics
We review recent efforts to explore the information on masses of heavy matter
particles, notably of the top quark and the Higgs boson, as encoded at the
quantum level in the renormalization group (RG) equations. The Standard Model
(SM) and the Minimal Supersymmetric Standard Model (MSSM) are considered in
parallel. First, the question is addressed to which extent the infrared (IR)
physics of the ``top-down'' RG flow is independent of the ultraviolet (UV)
physics. The central issues are i) IR attractive fixed point values for the top
and the Higgs mass, the most outstanding one being m_t=O(190 GeV)sin(beta) in
the MSSM, ii) IR attractive relations between parameters, the most prominent
ones being an IR fixed top-Higgs mass relation in the SM, leading to m_H=O(156)
GeV for the experimental top mass, and an IR fixed relation between the top
mass and tan(beta) in the MSSM, and iii) an analytical assessment of their
respective strengths of attraction. The triviality and vacuum stability bounds
on the Higgs and top masses in the SM and the upper bound on the lightest Higgs
boson mass in the MSSM are reviewed. The mathematical backbone, the rich
structure of IR attractive fixed points, lines, surfaces,... in the
multiparameter space, is made transparent. Interesting hierarchies emerge, most
remarkably: IR attraction in the MSSM is systematically stronger than in the
SM. Tau-bottom-(top) Yukawa coupling unification in supersymmetric grand
unified theories and its power to focus the ``top-down'' RG flow into the IR
top mass fixed point resp. onto the IR fixed line in the m_t-tan(beta) plane is
reviewed. The program of reduction of parameters, a search for RG invariant
relations between couplings, guided by the requirement of asymptotically free
couplings in the UV limit,is summarized; its interrelations with the search forComment: review, 112 pages, 39 figures and 15 figures in a table; one LaTeX
file, 50 postscript files; LaTeX uses style files epsfig.sty, rotating.sty,
dina4p.sty; to be published in Progress in Particle and Nuclear Physics, Vol.
37, 1996, copyright Elsevier Science Lt
The Impact of Conditional Cash Transfers on Marriage and Divorce
A growing number of less-developed countries have introduced conditional cash transfer programs in which funds are targeted to women. Economic models of the family suggest that these transfer programs may lead to marital turnover among program beneficiaries. We use data from the experimental evaluation of the PROGRESA program in Mexico to provide new evidence on the short-run impacts of targeted transfers on couples’ union dissolution and individuals’ new union formation decisions. We find that, although the overall share of women in union does not change as a result of the program, marital turnover increases. Intact families eligible for the transfers experienced a modest (0.32 percentage points) increase in separation rates, with most of the effect concentrated among young and relatively educated women households. In contrast, young single women with low educational attainment levels experienced a substantial increase in new union formation rates. The marital transition patterns are consistent with the workhorse economic model of the marriage market – individuals with the greatest prospects to start new unions and those who may become more attractive in the marriage market are more likely to transition out of existing relationships and form new ones.conditional cash transfers; welfare policy; marriage; divorce
Low Energy Precision Test of Supersymmetry
Supersymmetry (SUSY) remains one of the leading candidates for physics beyond
the Standard Model, and the search for SUSY will be a central focus of future
collider experiments. Complementary information on the viability and character
of SUSY can be obtained via the analysis of precision electroweak measurements.
In this review, we discuss the prospective implications for SUSY of present and
future precision studies at low energy.Comment: 118 pages, review pape
Improvements on Device Independent and Semi-Device Independent Protocols of Randomness Expansion
To generate genuine random numbers, random number generators based on quantum
theory are essential. However, ensuring that the process used to produce
randomness meets desired security standards can pose challenges for traditional
quantum random number generators. This thesis delves into Device Independent
(DI) and Semi-Device Independent (semi-DI) protocols of randomness expansion,
based on a minimal set of experimentally verifiable security assumptions. The
security in DI protocols relies on the violation of Bell inequalities, which
certify the quantum behavior of devices. The semi-DI protocols discussed in
this thesis require the characterization of only one device - a power meter.
These protocols exploit the fact that quantum states can be prepared such that
they cannot be distinguished with certainty, thereby creating a randomness
resource. In this study, we introduce enhanced DI and semi-DI protocols that
surpass existing ones in terms of output randomness rate, security, or in some
instances, both. Our analysis employs the Entropy Accumulation Theorem (EAT) to
determine the extractable randomness for finite rounds. A notable contribution
is the introduction of randomness expansion protocols that recycle input
randomness, significantly enhancing finite round randomness rates for DI
protocols based on the CHSH inequality violation. In the final section of the
thesis, we delve into Generalized Probability Theories (GPTs), with a focus on
Boxworld, the largest GPT capable of producing correlations consistent with
relativity. A tractable criterion for identifying a Boxworld channel is
presented.Comment: This PhD thesis consists of 212 pages, with 16 figures and presents
content that intersects with the author's previously published work R.
Bhavsar, S. Ragy, and R. Colbeck. Improved device independent randomness
expansion rates using two sided randomness. New Journal of Physics 25.9
(2023): 09303
Scalable Realtime Rendering and Interaction with Digital Surface Models of Landscapes and Cities
Interactive, realistic rendering of landscapes and cities differs substantially from classical terrain rendering. Due to the sheer size and detail of the data which need to be processed, realtime rendering (i.e. more than 25 images per second) is only feasible with level of detail (LOD) models. Even the design and implementation of efficient, automatic LOD generation is ambitious for such out-of-core datasets considering the large number of scales that are covered in a single view and the necessity to maintain screen-space accuracy for realistic representation. Moreover, users want to interact with the model based on semantic information which needs to be linked to the LOD model. In this thesis I present LOD schemes for the efficient rendering of 2.5d digital surface models (DSMs) and 3d point-clouds, a method for the automatic derivation of city models from raw DSMs, and an approach allowing semantic interaction with complex LOD models. The hierarchical LOD model for digital surface models is based on a quadtree of precomputed, simplified triangle mesh approximations. The rendering of the proposed model is proved to allow real-time rendering of very large and complex models with pixel-accurate details. Moreover, the necessary preprocessing is scalable and fast. For 3d point clouds, I introduce an LOD scheme based on an octree of hybrid plane-polygon representations. For each LOD, the algorithm detects planar regions in an adequately subsampled point cloud and models them as textured rectangles. The rendering of the resulting hybrid model is an order of magnitude faster than comparable point-based LOD schemes. To automatically derive a city model from a DSM, I propose a constrained mesh simplification. Apart from the geometric distance between simplified and original model, it evaluates constraints based on detected planar structures and their mutual topological relations. The resulting models are much less complex than the original DSM but still represent the characteristic building structures faithfully. Finally, I present a method to combine semantic information with complex geometric models. My approach links the semantic entities to the geometric entities on-the-fly via coarser proxy geometries which carry the semantic information. Thus, semantic information can be layered on top of complex LOD models without an explicit attribution step. All findings are supported by experimental results which demonstrate the practical applicability and efficiency of the methods
A Sign-to-Speech Translation System
This thesis describes sign-to-speech translation using neural networks. Sign language translation is an interesting but difficult problem for which neural network techniques seem promising because of their ability to adjust to the user\u27s hand movements, which is not possible to do by most other techniques. However, even using neural networks and artificial sign languages, the translation is hard, and the best-known system, that of Fels & Hinton (1993), is capable of translating only 66 root words and 203 words including their conjugations. This research improves their results to 790 root signs and 2718 words including their conjugations while preserving a high accuracy (i.e., over 93 %) in translation. The use of matcher neural networks (Revesz 1989, 1990) and asymmetric Hamming distances are the key sources of improvement. This research aims at providing a means of communication for deaf people.
Adviser: Peter Z. Reves
Modulated Rashba interaction in a quantum wire: Spin and charge dynamics
It was recently shown that a spatially modulated Rashba spin-orbit coupling
in a quantum wire drives a transition from a metallic to an insulating state
when the wave number of the modulation becomes commensurate with the Fermi wave
length of the electrons in the wire. It was suggested that the effect may be
put to practical use in a future spin transistor design. In the present article
we revisit the problem and present a detailed analysis of the underlying
physics. First, we explore how the build-up of charge density wave correlations
in the quantum wire due to the periodic gate configuration that produces the
Rashba modulation influences the transition to the insulating state. The
interplay between the modulations of the charge density and that of the
spin-orbit coupling turns out to be quite subtle: Depending on the relative
phase between the two modulations, the joint action of the Rashba interaction
and charge density wave correlations may either enhance or reduce the Rashba
current blockade effect. Secondly, we inquire about the role of the Dresselhaus
spin-orbit coupling that is generically present in a quantum wire embedded in
semiconductor heterostructure. While the Dresselhaus coupling is found to work
against the current blockade of the insulating state, the effect is small in
most materials. Using an effective field theory approach, we also carry out an
analysis of effects from electron- electron interactions, and show how the
single-particle gap in the insulating state can be extracted from the more
easily accessible collective charge and spin excitation thresholds. The
smallness of the single-particle gap together with the anti-phase relation
between the Rashba and chemical potential modulations pose serious difficulties
for realizing a Rashba-controlled current switch in an InAs-based device. Some
alternative designs are discussed.Comment: 20 pages, 6 figure
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