1,520 research outputs found
The Herschel view of the on-going star formation in the Vela-C molecular cloud
As part of the Herschel guaranteed time key program 'HOBYS', we present the
photometric survey of the star forming region Vela-C, one of the nearest sites
of low-to-high-mass star formation in the Galactic plane. Vela-C has been
observed with PACS and SPIRE in parallel mode between 70 um and 500 um over an
area of about 3 square degrees. A photometric catalogue has been extracted from
the detections in each band, using a threshold of 5 sigma over the local
background. Out of this catalogue we have selected a robust sub-sample of 268
sources, of which 75% are cloud clumps and 25% are cores. Their Spectral Energy
Distributions (SEDs) have been fitted with a modified black body function. We
classify 48 sources as protostellar and 218 as starless. For two further
sources, we do not provide a secure classification, but suggest they are Class
0 protostars.
From SED fitting we have derived key physical parameters. Protostellar
sources are in general warmer and more compact than starless sources. Both
these evidences can be ascribed to the presence of an internal source(s) of
moderate heating, which also causes a temperature gradient and hence a more
peaked intensity distribution. Moreover, the reduced dimensions of protostellar
sources may indicate that they will not fragment further. A virial analysis of
the starless sources gives an upper limit of 90% for the sources
gravitationally bound and therefore prestellar. We fit a power law N(logM) prop
M^-1.1 to the linear portion of the mass distribution of prestellar sources.
This is in between that typical of CO clumps and those of cores in nearby
star-forming regions. We interpret this as a result of the inhomogeneity of our
sample, which is composed of comparable fractions of clumps and cores.Comment: 9 pages, 7 figures, accepted by A&
Efficient non-malleable codes and key derivation for poly-size tampering circuits
Non-malleable codes, defined by Dziembowski, Pietrzak, and Wichs (ICS '10), provide roughly the following guarantee: if a codeword c encoding some message x is tampered to c' = f(c) such that c' ≠ c , then the tampered message x' contained in c' reveals no information about x. The non-malleable codes have applications to immunizing cryptosystems against tampering attacks and related-key attacks. One cannot have an efficient non-malleable code that protects against all efficient tampering functions f. However, in this paper we show 'the next best thing': for any polynomial bound s given a-priori, there is an efficient non-malleable code that protects against all tampering functions f computable by a circuit of size s. More generally, for any family of tampering functions F of size F ≤ 2s , there is an efficient non-malleable code that protects against all f in F . The rate of our codes, defined as the ratio of message to codeword size, approaches 1. Our results are information-theoretic and our main proof technique relies on a careful probabilistic method argument using limited independence. As a result, we get an efficiently samplable family of efficient codes, such that a random member of the family is non-malleable with overwhelming probability. Alternatively, we can view the result as providing an efficient non-malleable code in the 'common reference string' model. We also introduce a new notion of non-malleable key derivation, which uses randomness x to derive a secret key y = h(x) in such a way that, even if x is tampered to a different value x' = f(x) , the derived key y' = h(x') does not reveal any information about y. Our results for non-malleable key derivation are analogous to those for non-malleable codes. As a useful tool in our analysis, we rely on the notion of 'leakage-resilient storage' of Davì, Dziembowski, and Venturi (SCN '10), and, as a result of independent interest, we also significantly improve on the parameters of such schemes
Finite Time Stability of Linear Control Systems with Multiple Delays
In this paper, we considered finite time stability of a class of linear control systems. By using suitable matrix measures and Coppel’s inequality a bound for the solution of the linear control system with multiple delays in the state is determined. A sufficient delay dependent conditions for finite time stability of linear control system with delay are derived. Key words: Linear systems, control systems, stability, time delay, Coppel’s inequalit
Skewness risk and bond prices
Statistical evidence is reported that even outside disaster periods, agents face negative consumption skewness, as well as positive inflation skewness. Quantitative implications of skewness risk for nominal loan contracts in a pure exchange economy are
derived. Key modeling assumptions are Epstein-Zin preferences for traders and asymmetric distributions for consumption and inflation innovations. The model is solved
using a third-order perturbation and estimated by the simulated method of moments.
Results show that skewness risk accounts for 6 to 7 percent of the risk premia depending
on the bond maturity
On Secure Implementation of an IHE XUA-Based Protocol for Authenticating Healthcare Professionals
The importance of the Electronic Health Record (EHR) has been addressed in recent years by governments and institutions.Many large scale projects have been funded with the aim to allow healthcare professionals to consult patients data. Properties such as confidentiality, authentication and authorization are the key for the success for these projects. The Integrating the Healthcare Enterprise (IHE) initiative promotes the coordinated use of established standards for authenticated and secure EHR exchanges among clinics and hospitals. In particular, the IHE integration profile named XUA permits to attest user identities by relying on SAML assertions, i.e. XML documents containing authentication statements. In this paper, we provide a formal model for the secure issuance of such an assertion. We first specify the scenario using the process calculus COWS and then analyse it using the model checker CMC. Our analysis reveals a potential flaw in the XUA profile when using a SAML assertion in an unprotected network. We then suggest a solution for this flaw, and model check and implement this solution to show that it is secure and feasible
Fluctuation Theorem in Rachet System
Fluctuation Theorem(FT) has been studied as far from equilibrium theorem,
which relates the symmetry of entropy production. To investigate the
application of this theorem, especially to biological physics, we consider the
FT for tilted rachet system. Under, natural assumption, FT for steady state is
derived.Comment: 6 pages, 2 figure
Поняття суверенітету держави у міжнародному праві
Проаналізовано підходи до визначення суверенітету у вітчизняній та зарубіжній міжнародно-правовій науці. Виведено поняття суверенітету держави через аналіз теорії та історії явища. Ключові слова: суверенітет, поняття і явище, влада, верховенство і незалежність, міжнародне право.В статье проанализированы подходы к определению суверенитета в отечественной международно-правовой науке. Выведено понятие суверенитета государства через анализ истории теории и истории явления. Ключевые слова: суверенитет, понятие и явление, власть, верховенство и независимость, способность, международное право.In the article approaches of definition of the state sovereignty in the native scholarship of International Law are analyzed. The definition of state sovereignty from the analysis of the history of theory and the history of appearance is derived. Key words: Sovereignty, Notion and Phenomenon, Authority, Supremacy and Independence, Ability, International Law
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