16,674 research outputs found
Comment on: "Measuring a Photonic Qubit without Destroying It"
Recently, Pryde et al reported the demonstration of a quantum non-demolition
scheme for single-photon polarization states with linear optics and projective
measurements [Phys. Rev. Lett. 92, 190402 (2004)]. Here, we argue that their
interpretation of the experiment is inconsistent with the fidelity measure they
use.Comment: one page, no figure
The hexagonal versus the square lattice
We establish Schmutz Schaller's conjecture that the hexagonal lattice is
`better' than the square lattice.
Schmutz Schaller (Bulletin of the AMS 35 (1998), p. 201), motivated by
considerations from hyperbolic geometry, conjectured that in dimensions 2 to 8
the best known lattice sphere packings have `maximal lengths' and goes on to
write: "In dimension 2 the conjecture means in particular that the hexagonal
lattice is `better' than the square lattice. More precisely, let 0<h_1<h_2<...
be the positive integers, listed in ascending order, which can be written as
h_i=x^2+3y^2 for integers x and y. Let 0<q_1<q_2<... be the positive integers,
listed in ascending order, which can be written as q_i=x^2+y^2 for integers x
and y. Then the conjecture is that q_i<=h_i for i=1,2,3,..."
Our proof requires computational prime number theory in combination with
methods from a preprint of the first author (to appear in Math. Comp.),
arXiv:math.NT/0112100.Comment: 24 pages, 6 figures, 2 table
A Two-Process Model for Control of Legato Articulation Across a Wide Range of Tempos During Piano Performance
Prior reports indicated a non-linear increase in key overlap times (KOTs) as tempo slows for scales/arpeggios performed at internote intervals (INIs) of I00-1000 ms. Simulations illustrate that this function can be explained by a two-process model. An oscillating neural network based on dynamics of the vector-integration-to-endpoint model for central generation of voluntary actions, allows performers to compute an estimate of the time remaining before the oscillator's next cycle onset. At fixed successive threshold values of this estimate they first launch keystroke n+l and then lift keystroke n. As tempo slows, time required to pass between threshold crossings elongates, and KOT increases. If only this process prevailed, performers would produce longer than observed KOTs at the slowest tempo. The full data set is explicable if subjects lift keystroke n whenever they cross the second threshold or receive sensory feedback from stroke n+l, whichever comes earlier.Fulbright grant; Office of Naval Research (N00014-92-J-1309, N0014-95-1-0409
A case of epigastric heteropagus twinning with other congenital abnormalities in a Chihuahua puppy
A two-year-old Chihuahua was presented on day 58 of pregnancy due to very marked abdominal distension. A cesarean section was performed and five normal and one clearly abnormal puppy were delivered. Examination of the abnormal puppy revealed a combination of congenital anomalies including epigastric heteropagus twinning. The autosite showed focal cranial aplasia cutis, anasarca, lissencephaly, palatoschisis, sternal agenesis and eventeratio (gastroschisis/schistocoelia). The partly formed parasitic twin was attached at the sternal region of the autosite and demonstrated four formed limbs, atresia rectum, atresia ani, a single kidney, tail agenesis and atresia vulvae. To the authors' knowledge, this is only the third reported case of heteropagus conjoined twinning in the dog and the first reported case of canine epigastric heteropagus twinning. In addition, there appear to be no reports in the veterinary literature noting an association with conjoined twinning in the dog with focal cranial aplasia cutis, eventeratio, lissencephaly, palatoschisis and anasarca. An in-depth literature review was hampered by the lack of a uniform nomenclature to identify this type of conjoined twinning
Controlling platinum, ruthenium, and osmium reactivity for anticancer drug design
The main task of the medicinal chemist is to design molecules that interact
specifically with derailed or degenerating processes in a diseased organism,
translating the available knowledge of pathobiochemical and physiological data into
chemically useful information and structures. Current knowledge of the biological
and chemical processes underlying diseases is vast and rapidly expanding. In
particular the unraveling of the genome in combination with, for instance, the rapid
development of structural biology has led to an explosion in available information and
identification of new targets for chemotherapy. The task of translating this wealth of
data into active and selective new drugs is an enormous, but realistic, challenge. It
requires knowledge from many different fields, including molecular biology,
chemistry, pharmacology, physiology, and medicine and as such requires a truly
interdisciplinary approach.
Ultimately, the goal is to design molecules that satisfy all the requirements for a
candidate drug to function therapeutically. Therapeutic activity can then be achieved
by an understanding of and control over structure and reactivity of the candidate drug
through molecular manipulation
Atomic Diffusion and Mixing in Old Stars V: A deeper look into the Globular Cluster NGC 6752
Abundance trends in heavier elements with evolutionary phase have been shown
to exist in the globular cluster NGC 6752 [Fe/H]=-1.6. These trends are a
result of atomic diffusion and additional (non-convective) mixing. Studying
such trends can provide us with important constraints on the extent to which
diffusion modifies the internal structure and surface abundances of solar-type,
metal-poor stars. Taking advantage of a larger data sample, we investigate the
reality and the size of these abundance trends and address questions and
potential biases associated with the various stellar populations that make up
NGC6752. Based on uvby Str\"omgren photometry, we are able to separate three
stellar populations in NGC 6752 along the evolutionary sequence from the base
of the red giant branch down to the turnoff point. We find weak systematic
abundance trends with evolutionary phase for Ca, Ti, and Fe which are best
explained by stellar-structure models including atomic diffusion with efficient
additional mixing. We derive a new value for the initial lithium abundance of
NGC 6752 after correcting for the effect of atomic diffusion and additional
mixing which falls slightly below the predicted standard BBN value. We find
three stellar populations by combining photometric and spectroscopic data of
194 stars in the globular cluster NGC 6752. Abundance trends for groups of
elements, differently affected by atomic diffusion and additional mixing, are
identified. Although the statistical significance of the individual trends is
weak, they all support the notion that atomic diffusion is operational along
the evolutionary sequence of NGC 6752.Comment: 15 pages, 11 figures, 2 online table
The Impact of the Sarbanes-Oxley Act (SOX) on the Cost of Equity Capital of S&P Firms
This study examines the impact of SOX on the cost of equity capital for small and large S&P firms. The provisions of SOX aim to improve internal control systems and reduce information asymmetry by improving corporate governance systems and increasing transparency. Using a fixed-effects regression model, our findings suggest that the cost of equity capital has decreased post-SOX for the overall sample of firms, but more specifically for the small firms, which are usually associated with poor internal control systems and high information asymmetry. Collectively, our results provide evidence that SOX has had a positive impact on firms
Stereo block copolymers of L- and D-lactides
Sequential diblock copolymers composed of L- and D-lactic acid residues were synthesized through a living ring-opening polymerization of L- and D-lactide initiated by aluminium tris(2-propanolate). The composition of the block copolymers was varied by changing the reaction conditions and monomer over initiator ratio and confirmed by 1H NMR analysis, molecular weight determination and optical rotation measurements. Molecular weights ranged from 1,3 to 2,0 · 104 with 1,2 < Mw/Mn < 1,4. Stereocomplex formation in all block copolymers was determined using differential scanning calorimetry showing melting temperatures of about 205°C
Epidemics on random intersection graphs
In this paper we consider a model for the spread of a stochastic SIR
(Susceptible Infectious Recovered) epidemic on a network of
individuals described by a random intersection graph. Individuals belong to a
random number of cliques, each of random size, and infection can be transmitted
between two individuals if and only if there is a clique they both belong to.
Both the clique sizes and the number of cliques an individual belongs to follow
mixed Poisson distributions. An infinite-type branching process approximation
(with type being given by the length of an individual's infectious period) for
the early stages of an epidemic is developed and made fully rigorous by proving
an associated limit theorem as the population size tends to infinity. This
leads to a threshold parameter , so that in a large population an epidemic
with few initial infectives can give rise to a large outbreak if and only if
. A functional equation for the survival probability of the
approximating infinite-type branching process is determined; if , this
equation has no nonzero solution, while if , it is shown to have
precisely one nonzero solution. A law of large numbers for the size of such a
large outbreak is proved by exploiting a single-type branching process that
approximates the size of the susceptibility set of a typical individual.Comment: Published in at http://dx.doi.org/10.1214/13-AAP942 the Annals of
Applied Probability (http://www.imstat.org/aap/) by the Institute of
Mathematical Statistics (http://www.imstat.org
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