7,041 research outputs found
Split-Stirling-cycle displacer linear-electric drive
The retrofit of a 1/4-W split-Stirling cooler with a linear driven on the displacer was achieved and its performance characterized. The objective of this work was to demonstrate that a small linear motor could be designed to meet the existing envelope specifications of the cooler and that an electric linear drive on the displacer could improve the cooler's reliability and performance. The paper describes the characteristics of this motor and presents cooler test results
A tight lower bound instance for k-means++ in constant dimension
The k-means++ seeding algorithm is one of the most popular algorithms that is
used for finding the initial centers when using the k-means heuristic. The
algorithm is a simple sampling procedure and can be described as follows: Pick
the first center randomly from the given points. For , pick a point to
be the center with probability proportional to the square of the
Euclidean distance of this point to the closest previously chosen
centers.
The k-means++ seeding algorithm is not only simple and fast but also gives an
approximation in expectation as shown by Arthur and Vassilvitskii.
There are datasets on which this seeding algorithm gives an approximation
factor of in expectation. However, it is not clear from these
results if the algorithm achieves good approximation factor with reasonably
high probability (say ). Brunsch and R\"{o}glin gave a dataset where
the k-means++ seeding algorithm achieves an approximation ratio
with probability that is exponentially small in . However, this and all
other known lower-bound examples are high dimensional. So, an open problem was
to understand the behavior of the algorithm on low dimensional datasets. In
this work, we give a simple two dimensional dataset on which the seeding
algorithm achieves an approximation ratio with probability
exponentially small in . This solves open problems posed by Mahajan et al.
and by Brunsch and R\"{o}glin.Comment: To appear in TAMC 2014. arXiv admin note: text overlap with
arXiv:1306.420
The Azimuthal Asymmetry at large p_t seem to be too large for a ``Jet Quenching''
We discuss simple generic model of ``jet quenching'' in which matter
absorption is defined by one parameter. We show that as absorption grows, the
azimuthal asymmetry v_2 grows as well, reaching the finite limit with a simple
geometric interpretation. It turns out, that this limit is still below the
experimental values for 6 > p_t > 2 GeV, according to preliminary data from
STAR experiment at RHIC. We thus conclude that ``jet quenching'' models alone
cannot account for the observed phenomenon, and speculate about alternative
scenarios.Comment: 3 pages, 2 figs, 1 table. The final version contaning note added in
proofs for PRC, which reflects experimental development which seem to suggest
that the geometrical model for v2 is in fact correct description of data at
pt=2-10 Ge
The Epsilon Calculus and Herbrand Complexity
Hilbert's epsilon-calculus is based on an extension of the language of
predicate logic by a term-forming operator . Two fundamental
results about the epsilon-calculus, the first and second epsilon theorem, play
a role similar to that which the cut-elimination theorem plays in sequent
calculus. In particular, Herbrand's Theorem is a consequence of the epsilon
theorems. The paper investigates the epsilon theorems and the complexity of the
elimination procedure underlying their proof, as well as the length of Herbrand
disjunctions of existential theorems obtained by this elimination procedure.Comment: 23 p
Amarynthos 2014.
dans Reber Karl et al., "Aktivitäten der Schweizerischen Archäologischen Schule in Griechenland 2014", p. 129-152International audienc
Risk factors for low urinary citrate in calcium nephrolithiasis: low vegetable fibre intake and low urine volume to be added to the list
Risk factors for low urinary citrate excretion were assessed in 34 consecutive male recurrent idiopathic calcium stone formers (RCSF) who collected two 24-h urines while on free-choice diet. Overt hypocitraturia (hypo-cit) was defined as UCit×V<1.70 mmol/day, and ‘low' citraturia (low-cit) as UCit×V between 1.70 and 2.11 mmol/day. Twenty-three RCSF had normocitraturia (normo-cit), six low-cit and five hypo-cit. UCit×V positively correlated with urine volume (VOLUME, r=0.44, P=0.009), vegetable fibre intake (fibers, r=0.46, P=0.009) and GI-alkali absorption (alkali, r=0.47, P=0.006), and volume, fibres and alkali tended to be lower among RCSF with low-/hypo-cit. A 3-day NH4Cl loading test (0.95 mEq/kg BW daily in 3 doses) was performed in RCSF as well as in 14 age-matched healthy male controls (C). On a plot of urine pH versus serum bicarbonate, 10 of 11 RCSF with low-/hypo-cit, but only six of 23 with normo-cit (P=0.0004) fell off the normal range, indicating incomplete RTA. Two or more risk factors simultaneously occurred in only four of 23 RCSF with normo-cit, but in eight of 11 with low-/hypo-cit (P= 0.002). In conclusion, incomplete RTA is the most prevalent risk factor for low-/hypo-cit in RCSF, and decreases in vegetable fibres and urine volume emerge as two new risk factors for low urinary CI
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