35,660 research outputs found
An approximate solution for interlaminar stresses in laminated composites: Applied mechanics program
An approximate solution for interlaminar stresses in finite width, laminated composites subjected to uniform extensional, and bending loads is presented. The solution is based upon the principle of minimum complementary energy and an assumed, statically admissible stress state, derived by considering local material mismatch effects and global equilibrium requirements. The stresses in each layer are approximated by polynomial functions of the thickness coordinate, multiplied by combinations of exponential functions of the in-plane coordinate, expressed in terms of fourteen unknown decay parameters. Imposing the stationary condition of the laminate complementary energy with respect to the unknown variables yields a system of fourteen non-linear algebraic equations for the parameters. Newton's method is implemented to solve this system. Once the parameters are known, the stresses can be easily determined at any point in the laminate. Results are presented for through-thickness and interlaminar stress distributions for angle-ply, cross-ply (symmetric and unsymmetric laminates), and quasi-isotropic laminates subjected to uniform extension and bending. It is shown that the solution compares well with existing finite element solutions and represents an improved approximate solution for interlaminar stresses, primarily at interfaces where global equilibrium is satisfied by the in-plane stresses, but large local mismatch in properties requires the presence of interlaminar stresses
The Potential of Learned Index Structures for Index Compression
Inverted indexes are vital in providing fast key-word-based search. For every
term in the document collection, a list of identifiers of documents in which
the term appears is stored, along with auxiliary information such as term
frequency, and position offsets. While very effective, inverted indexes have
large memory requirements for web-sized collections. Recently, the concept of
learned index structures was introduced, where machine learned models replace
common index structures such as B-tree-indexes, hash-indexes, and
bloom-filters. These learned index structures require less memory, and can be
computationally much faster than their traditional counterparts. In this paper,
we consider whether such models may be applied to conjunctive Boolean querying.
First, we investigate how a learned model can replace document postings of an
inverted index, and then evaluate the compromises such an approach might have.
Second, we evaluate the potential gains that can be achieved in terms of memory
requirements. Our work shows that learned models have great potential in
inverted indexing, and this direction seems to be a promising area for future
research.Comment: Will appear in the proceedings of ADCS'1
Addressing spin transitions on 209Bi donors in silicon using circularly-polarized microwaves
Over the past decade donor spin qubits in isotopically enriched Si
have been intensely studied due to their exceptionally long coherence times.
More recently bismuth donor electron spins have become popular because Bi has a
large nuclear spin which gives rise to clock transitions (first-order
insensitive to magnetic field noise). At every clock transition there are two
nearly degenerate transitions between four distinct states which can be used as
a pair of qubits. Here it is experimentally demonstrated that these transitions
are excited by microwaves of opposite helicity such that they can be
selectively driven by varying microwave polarization. This work uses a
combination of a superconducting coplanar waveguide (CPW) microresonator and a
dielectric resonator to flexibly generate arbitrary elliptical polarizations
while retaining the high sensitivity of the CPW
Development of thermally stable phosphonitrile elastomers for advanced aerospace structures
Both high and low molecular weight, curable poly(fluoroalkoxy phosphazene) terpolymers were prepared. These terpolymers resulted from reaction of (Cl2PNn) polymer with alkoxides derived from CF3CH2OH and C3F7CH2OH, and an alkoxide derived from CH3CH(OH)C2H4OH. The terpolymers were crosslinked with polyisocyanates at room temperature. High molecular weight materials were converted into isocyanate prepolymers which as films underwent moisture cures at room temperature. Prepolymer solutions were stable for several days, and showed good adhesion. Also the effects of polymerization of (Cl2PN)3 were studied. Purified octachlorophosphazene, thiocyanate salts, or hydrogen chloride were employed in attempts to decrease molecular weight. Hydrogen chloride was found to be a good agent for preparation of low molecular weight poly(dichloro phosphazene)
Spin Coherence and N ESEEM Effects of Nitrogen-Vacancy Centers in Diamond with X-band Pulsed ESR
Pulsed ESR experiments are reported for ensembles of negatively-charged
nitrogen-vacancy centers (NV) in diamonds at X-band magnetic fields
(280-400 mT) and low temperatures (2-70 K). The NV centers in synthetic
type IIb diamonds (nitrogen impurity concentration ~ppm) are prepared with
bulk concentrations of cm to cm
by high-energy electron irradiation and subsequent annealing. We find that a
proper post-radiation anneal (1000C for 60 mins) is critically
important to repair the radiation damage and to recover long electron spin
coherence times for NVs. After the annealing, spin coherence times of T~ms at 5~K are achieved, being only limited by C nuclear spectral
diffusion in natural abundance diamonds. At X-band magnetic fields, strong
electron spin echo envelope modulation (ESEEM) is observed originating from the
central N nucleus. The ESEEM spectral analysis allows for accurate
determination of the N nuclear hypefine and quadrupole tensors. In
addition, the ESEEM effects from two proximal C sites (second-nearest
neighbor and fourth-nearest neighbor) are resolved and the respective C
hyperfine coupling constants are extracted.Comment: 10 pages, 5 figure
Time evolution of the Partridge-Barton Model
The time evolution of the Partridge-Barton model in the presence of the
pleiotropic constraint and deleterious somatic mutations is exactly solved for
arbitrary fecundity in the context of a matricial formalism. Analytical
expressions for the time dependence of the mean survival probabilities are
derived. Using the fact that the asymptotic behavior for large time is
controlled by the largest matrix eigenvalue, we obtain the steady state values
for the mean survival probabilities and the Malthusian growth exponent. The
mean age of the population exhibits a power law decayment. Some Monte
Carlo simulations were also performed and they corroborated our theoretical
results.Comment: 10 pages, Latex, 1 postscript figure, published in Phys. Rev. E 61,
5664 (2000
Unambiguous pure state identification without classical knowledge
We study how to unambiguously identify a given quantum pure state with one of
the two reference pure states when no classical knowledge on the reference
states is given but a certain number of copies of each reference quantum state
are presented. By the unambiguous identification, we mean that we are not
allowed to make a mistake but our measurement can produce an inconclusive
result. Assuming the two reference states are independently distributed over
the whole pure state space in a unitary invariant way, we determine the optimal
mean success probability for an arbitrary number of copies of the reference
states and a general dimension of the state space. It is explicitly shown that
the obtained optimal mean success probability asymptotically approaches that of
the unambiguous discrimination as the number of the copies of the reference
states increases.Comment: v3: 8 pages, minor corrections, journal versio
High bat (Chiroptera) diversity in the Early Eocene of India
The geographic origin of bats is still unknown, and fossils of earliest bats are rare and poorly diversified, with, maybe, the exception of Europe. The earliest bats are recorded from the Early Eocene of North America, Europe, North Africa and Australia where they seem to appear suddenly and simultaneously. Until now, the oldest record in Asia was from the Middle Eocene. In this paper, we report the discovery of the oldest bat fauna of Asia dating from the Early Eocene of the Cambay Formation at Vastan Lignite Mine in Western India. The fossil taxa are described on the basis of well-preserved fragments of dentaries and lower teeth. The fauna is highly diversified and is represented by seven species belonging to seven genera and at least four families. Two genera and five species are new. Three species exhibit very primitive dental characters, whereas four others indicate more advanced states. Unexpectedly, this fauna presents strong affinities with the European faunas from the French Paris Basin and the German Messel locality. This could result from the limited fossil record of bats in Asia, but could also suggest new palaeobiogeographic scenarios involving the relative position of India during the Early Eocene
What Have We Learned from Policy Transfer Research? Dolowitz and Marsh Revisited
Over the last decade, policy transfer has emerged as an important concept within public policy analysis, guiding both theoretical and empirical research spanning many venues and issue areas. Using Dolowitz and Marsh's 1996 stocktake as its starting point, this article reviews what has been learned by whom and for what purpose. It finds that the literature has evolved from its rather narrow, state-centred roots to cover many more actors and venues. While policy transfer still represents a niche topic for some researchers, an increasing number have successfully assimilated it into wider debates on topics such as globalisation, Europeanisation and policy innovation. This article assesses the concept's position in the overall ‘tool-kit’ of policy analysis, examines some possible future directions and reflects on their associated risks and opportunities
Evaluating Variable-Length Multiple-Option Lists in Chatbots and Mobile Search
In recent years, the proliferation of smart mobile devices has lead to the
gradual integration of search functionality within mobile platforms. This has
created an incentive to move away from the "ten blue links'' metaphor, as
mobile users are less likely to click on them, expecting to get the answer
directly from the snippets. In turn, this has revived the interest in Question
Answering. Then, along came chatbots, conversational systems, and messaging
platforms, where the user needs could be better served with the system asking
follow-up questions in order to better understand the user's intent. While
typically a user would expect a single response at any utterance, a system
could also return multiple options for the user to select from, based on
different system understandings of the user's intent. However, this possibility
should not be overused, as this practice could confuse and/or annoy the user.
How to produce good variable-length lists, given the conflicting objectives of
staying short while maximizing the likelihood of having a correct answer
included in the list, is an underexplored problem. It is also unclear how to
evaluate a system that tries to do that. Here we aim to bridge this gap. In
particular, we define some necessary and some optional properties that an
evaluation measure fit for this purpose should have. We further show that
existing evaluation measures from the IR tradition are not entirely suitable
for this setup, and we propose novel evaluation measures that address it
satisfactorily.Comment: 4 pages, in Proceeding of SIGIR 201
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