587 research outputs found
Proof of a conjecture of Polya on the zeros of successive derivatives of real entire functions
We prove Polya's conjecture of 1943: For a real entire function of order
greater than 2, with finitely many non-real zeros, the number of non-real zeros
of the n-th derivative tends to infinity with n. We use the saddle point method
and potential theory, combined with the theory of analytic functions with
positive imaginary part in the upper half-plane.Comment: 26 page
Normal Coordinates Describing Coupled Oscillations in the Gravitational Field
The motion of a local source inducing small oscillations in the gravitational
field is investigated and shown to exhibit pure rotational kinetic energy.
Should the net affect of these slow, revolving oscillations cause large-scale
rotations in spacetime it would certainly result in anomalous celestial
accelerations. When this angular rotational frequency of spacetime is applied
to the anomalous acceleration of the Pioneer 10/11 spacecrafts, the correlation
is promising.Comment: General Relativity and Gravitation Ref.: Ms. No. GERG-D-06-00077R1
accepted for publication October 06, 200
Can filesharers be triggered by economic incentives? Results of an experiment
Illegal filesharing on the internet leads to considerable financial losses for artists and copyright owners as well as producers and sellers of music. Thus far, measures to contain this phenomenon have been rather restrictive. However, there are still a considerable number of illegal systems, and users are able to decide quite freely between legal and illegal downloads because the latter are still difficult to sanction. Recent economic approaches account for the improved bargaining position of users. They are based on the idea of revenue-splitting between professional sellers and peers. In order to test such an innovative business model, the study reported in this article carried out an experiment with 100 undergraduate students, forming five small peer-to-peer networks.The networks were confronted with different economic conditions.The results indicate that even experienced filesharers hold favourable attitudes towards revenue-splitting.They seem to be willing to adjust their behaviour to different economic conditions
Measuring proper motions of isolated neutron stars with Chandra
The excellent spatial resolution of the Chandra observatory offers the
unprecedented possibility to measure proper motions at X-ray wavelength with
relatively high accuracy using as reference the background of extragalactic or
remote galactic X-ray sources. We took advantage of this capability to
constrain the proper motion of RX J0806.4-4123 and RX J0420.0-5022, two X-ray
bright and radio quiet isolated neutron stars (INSs) discovered by ROSAT and
lacking an optical counterpart. In this paper, we present results from a
preliminary analysis from which we derive 2 sigma upper limits of 76 mas/yr and
138 mas/yr on the proper motions of RX J0806.4-4123 and RX J0420.0-5022
respectively. We use these values together with those of other ROSAT discovered
INSs to constrain the origin, distance and evolutionary status of this
particular group of objects. We find that the tangential velocities of radio
quiet ROSAT neutron stars are probably consistent with those of 'normal'
pulsars. Their distribution on the sky and, for those having accurate proper
motion vectors, their possible birth places, all point to a local population,
probably created in the part of the Gould Belt nearest to the earth.Comment: 8 pages, 3 figures, to appear in Astrophysics and Space Science, in
the proceedings of "Isolated Neutron Stars: from the Interior to the
Surface", edited by D. Page, R. Turolla and S. Zan
Deregulated microRNAs in neurofibromatosis type 1 derived malignant peripheral nerve sheath tumors
Malignant peripheral nerve sheath tumors (MPNST) are aggressive cancers that occur spontaneously (sporadic MPNST) or from benign plexiform neurofibromas in neurofibromatosis type 1 (NF1) patients. MPNSTs metastasize easily, are therapy resistant and are frequently fatal. The molecular changes underlying the malignant transformation in the NF1 setting are incompletely understood. Here we investigate the involvement of microRNAs in this process. MicroRNA expression profiles were determined from a series of archival, paired samples of plexiform neurofibroma and MPNST. Ninety differentially expressed microRNAs were identified between the paired samples. Three downregulated microRNAs (let-7b-5p, miR-143-3p, miR-145-5p) and two upregulated microRNAs (miR135b-5p and miR-889-3p) in MPNST were selected for functional characterization. In general, their differential expression was validated in a relevant cell line panel but only partly in a series of unpaired, fresh frozen tumor samples. As part of the validation process we also analyzed microRNA expression profiles of sporadic MPNSTs observing that microRNA expression discriminates NF1-associated and sporadic MPNSTs. The role of microRNAs in cancer progression was examined in NF1-derived MPNST cell lines by transiently modulating microRNA levels. Our findings indicate that some microRNAs affect migratory and invasive capabilities and Wnt signaling activity but the effects are distinct in different cell lines. We conclude that miRNAs play essential regulatory roles in MPNST facilitating tumor progression
Finite-Temperature Transport in Finite-Size Hubbard Rings in the Strong-Coupling Limit
We study the current, the curvature of levels, and the finite temperature
charge stiffness, D(T,L), in the strongly correlated limit, U>>t, for Hubbard
rings of L sites, with U the on-site Coulomb repulsion and t the hopping
integral. Our study is done for finite-size systems and any band filling. Up to
order t we derive our results following two independent approaches, namely,
using the solution provided by the Bethe ansatz and the solution provided by an
algebraic method, where the electronic operators are represented in a
slave-fermion picture. We find that, in the U=\infty case, the
finite-temperature charge stiffness is finite for electronic densities, n,
smaller than one. These results are essencially those of spinless fermions in a
lattice of size L, apart from small corrections coming from a statistical flux,
due to the spin degrees of freedom. Up to order t, the Mott-Hubbard gap is
\Delta_{MH}=U-4t, and we find that D(T) is finite for n<1, but is zero at
half-filling. This result comes from the effective flux felt by the holon
excitations, which, due to the presence of doubly occupied sites, is
renormalized to
\Phi^{eff}=\phi(N_h-N_d)/(N_d+N_h), and which is zero at half-filling, with
N_d and N_h being the number of doubly occupied and empty lattice sites,
respectively. Further, for half-filling, the current transported by any
eigenstate of the system is zero and, therefore, D(T) is also zero.Comment: 15 pages and 6 figures; accepted for PR
News from the Muon (g-2) Experiment at BNL
The magnetic moment anomaly a_mu = (g_mu - 2) / 2 of the positive muon has
been measured at the Brookhaven Alternating Gradient Synchrotron with an
uncertainty of 0.7 ppm. The new result, based on data taken in 2000, agrees
well with previous measurements. Standard Model evaluations currently differ
from the experimental result by 1.6 to 3.0 standard deviations.Comment: Talk presented at RADCOR - Loops and Legs 2002, Kloster Banz,
Germany, September 8-13 2002, to be published in Nuclear Physics B (Proc.
Suppl.); 5 pages, 3 figure
Quantum algorithms for matrix scaling and matrix balancing
Matrix scaling and matrix balancing are two basic linear-algebraic problems with a wide variety of applications, such as approximating the permanent, and pre-conditioning linear systems to make them more numerically stable. We study the power and limitations of quantum algorithms for these problems. We provide quantum implementations of two classical (in both senses of the word) methods: Sinkhorn's algorithm for matrix scaling and Osborne's algorithm for matrix balancing. Using amplitude estimation as our main tool, our quantum implementations both run in time Ă(âmn/â4) for scaling or balancing an nĂn matrix (given by an oracle) with m non-zero entries to within â1-error â. Their classical analogs use time Ă(m/â2), and every classical algorithm for scaling or balancing with small constant â requires Ω(m) queries to the entries of the input matrix. We thus achieve a polynomial speed-up in terms of n, at the expense of a worse polynomial dependence on the obtained â1-error â. Even for constant â these problems are already non-trivial (and relevant in applications). Along the way, we extend the classical analysis of Sinkhorn's and Osborne's algorithm to allow for errors in the computation of marginals. We also adapt an improved analysis of Sinkhorn's algorithm for entrywise-positive matrices to the â1-setting, obtaining an Ă(n1.5/â3)-time quantum algorithm for â-â1-scaling. We also prove a lower bound, showing our quantum algorithm for matrix scaling is essentially optimal for constant â: every quantum algorithm for matrix scaling that achieves a constant â1-error w.r.t. uniform marginals needs Ω(â mn) queries
Improved Measurement of the Positive Muon Anomalous Magnetic Moment
A new measurement of the positive muon's anomalous magnetic moment has been
made at the Brookhaven Alternating Gradient Synchrotron using the direct
injection of polarized muons into the superferric storage ring. The angular
frequency difference omega_{a} between the angular spin precession frequency
omega_{s} and the angular orbital frequency omega_{c} is measured as well as
the free proton NMR frequency omega_{p}. These determine
R = omega_{a} / omega_{p} = 3.707~201(19) times 10^{-3}. With mu_{mu} /
mu_{p} = 3.183~345~39(10) this gives a_{mu^+} = 11~659~191(59) times 10^{-10}
(pm 5 ppm), in good agreement with the previous CERN and BNL measurements for
mu^+ and mu^-, and with the standard model prediction.Comment: 4 pages, 4 figures. accepted for publication in Phys. Rev. D62 Rapid
Communication
Whiteness and diasporic Irishness: nation, gender and class
Whiteness is often detached from the notion of diaspora in the recent flurry of interest in the phenomenon, yet it is a key feature of some of the largest and oldest displacements. This paper explores the specific contexts of white racial belonging and status over two centuries in two main destinations of the Irish diaspora, the USA and Britain. Its major contribution is a tracing of the untold story of âHow the Irish became white in Britainâ to parallel and contrast with the much more fully developed narrative in the USA. It argues that, contrary to popular belief, the racialisation of the Irish in England did not fade away at the end of the nineteenth century but became transmuted in new forms which have continued to place the âwhiteâ Irish outside the boundaries of the English nation. These have been strangely ignored by social scientists, who conflate Irishness and working-class identities in England without acknowledging the distinctive contribution of Irish backgrounds to constructions of class difference. Gender locates Irish women and men differently in relation to these class positions, for example allowing mothers to be blamed for the perpetuation of the underclass. Class and gender are also largely unrecognised dimensions of Irish ethnicity in the USA, where the presence of âpoor whiteâ neighbourhoods continues to challenge the iconic story of Irish upward mobility. Irishness thus remains central to the construction of mainstream âwhiteâ identities in both the USA and Britain into the twenty-first century
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