10,697 research outputs found
Asymmetric Distributed Trust
Quorum systems are a key abstraction in distributed fault-tolerant computing for capturing trust assumptions. They can be found at the core of many algorithms for implementing reliable broadcasts, shared memory, consensus and other problems. This paper introduces asymmetric Byzantine quorum systems that model subjective trust. Every process is free to choose which combinations of other processes it trusts and which ones it considers faulty. Asymmetric quorum systems strictly generalize standard Byzantine quorum systems, which have only one global trust assumption for all processes. This work also presents protocols that implement abstractions of shared memory and broadcast primitives with processes prone to Byzantine faults and asymmetric trust. The model and protocols pave the way for realizing more elaborate algorithms with asymmetric trust
Proton Heating in Solar Wind Compressible Turbulence with Collisions between Counter-propagating Waves
Magnetohydronamic turbulence is believed to play a crucial role in heating
the laboratorial, space, and astrophysical plasmas. However, the precise
connection between the turbulent fluctuations and the particle kinetics has not
yet been established. Here we present clear evidence of plasma turbulence
heating based on diagnosed wave features and proton velocity distributions from
solar wind measurements by the Wind spacecraft. For the first time, we can
report the simultaneous observation of counter-propagating magnetohydrodynamic
waves in the solar wind turbulence. Different from the traditional paradigm
with counter-propagating Alfv\'en waves, anti-sunward Alfv\'en waves (AWs) are
encountered by sunward slow magnetosonic waves (SMWs) in this new type of solar
wind compressible turbulence. The counter-propagating AWs and SWs correspond
respectively to the dominant and sub-dominant populations of the imbalanced
Els\"asser variables. Nonlinear interactions between the AWs and SMWs are
inferred from the non-orthogonality between the possible oscillation direction
of one wave and the possible propagation direction of the other. The associated
protons are revealed to exhibit bi-directional asymmetric beams in their
velocity distributions: sunward beams appearing in short and narrow patterns
and anti-sunward broad extended tails. It is suggested that multiple types of
wave-particle interactions, i.e., cyclotron and Landau resonances with AWs and
SMWs at kinetic scales, are taking place to jointly heat the protons
perpendicularly and parallel
Novel Contract Signature based on Key Exchange
A contract signature is a particular form of digital multi-signature that only involves two signers. Contract signing plays a critical role in any business transaction, particularly in situations where the involved parties do not trust each other. One of the most significant concerns in exchange signatures is the fraudulent and unfair exchange, which occurs when one party gets the signature of another party without giving his own signature. In the view of these security concerns, this thesis presents a secure and fair contract signature scheme based on key exchange protocol. The security and protection of the proposed scheme is based on solving hard computational assumptions such as discrete logarithm problem (DLP). The proposed protocol is abuse-free. The proposed scheme targets to have lesser computational overhead and high-security features than existing scheme[1]. The proposed scheme has wide application in real life scenarios, such as in electronic cash system
SPECTRASAT: A concept for the collection of global directional wave spectra
The synthetic aperture radar (SAR) imagery from SEASAT revealed a rich tapestry of backscatter patterns from the surface of the ocean. Although still far from being fully understood, these patterns occurred on nearly all spatial scales accessible to the SAR, that is from its spatial resolution of 25 m to its full swath width of 100 km. Futhermore, the backscatter signature appear to reveal a large variety of atmospheric and oceanic processes that occur above, at, and below the ocean surface. Proper interpretation of these signatures of varying scales with respect to their underlying geophysical causes is a major objective of SAR ocean research. Even now, however, it is clear that SAR offers a unique means to monitor wind and waves over global scales. A properly designed, configured, and complimented orbiting SAR system should yield substantial improvements in operational forecasts vital to marine activities. Since wind and wave information is optimally extracted in the spectral domain, the name SPECTRASAT is proposed for this global collection scheme
Pendekatan konstruktif dalam inovasi pengajaran dan pembelajaran Bahasa Melayu di Kolej Vokasional
Pendekatan konstruktif adalah pendekatan pengajaran dan pembelajaran yang
berpusatkan pelajar manakala inovasi pengajaran pula dikaitkan dengan kaedah
pengajaran yang terbaru demi mengukuhkan pemahaman pelajar. Pembelajaran
berasaskan pendekatan konstruktif merupakan elemen yang penting dan perlu
difahami oleh guru-guru bagi memantapkan proses pengajaran dan pembelajaran
sesuai dengan peredaran masa dan menjayakan proses tranformasi pendidikan
negara. Objektif kajian ini dijalankan untuk mengenal pasti pemahaman guru-guru
bahasa Melayu berkaitan inovasi, mengenal pasti perbezaan yang wujud antara guru
lelaki dan guru perempuan dalam mengamalkan inovasi, pengkaji juga melihat
adakah wujud perbezaan antara guru baru dan guru yang sudah berpengalaman
dalam aspek mengaplikasikan inovasi serta mengenal pasti kekangan-kekangan yang
dialami oleh para guru untuk mengaplikasikan inovasi di sekolah. Seramai 63 orang
guru bahasa Melayu dari lapan buah kolej vokasional telah dipilih sebagai responden
dalam kajian ini. Data dianalisis menggunakan perisian Winsteps 3.69.1.11 dengan
pendekatan Model Pengukuran Rasch. Hasil analisis menunjukkan bahawa guru�guru bahasa Melayu memahami kepentingan inovasi dalam pengajaran dan
pembelajaran. Hasil kajian juga menunjukkan guru-guru perempuan lebih banyak
menerapkan unsur inovasi dalam pengajaran berbanding guru lelaki. Walaupun
begitu, aspek pengalaman tidak menunjukkan perbezaan dari segi pengamalan
inovasi sama ada guru baru ataupun guru yang sudah berpengalaman. Pengkaji juga
mengenal pasti beberapa kekangan yang dialami oleh guru-guru untuk mengamalkan
inovasi ini. Sebagai langkah untuk menangani masalah berkenaan, beberapa
cadangan telah dikemukakan oleh pengkaji bagi memastikan guru-guru dapat
merealisasikan proses pengajaran berkesan dengan penerapan inovasi mengikut
model pendekatan konstruktif. Pengkaji berharap, kajian ini dapat dijadikan sebagai
satu panduan kepada pelaksana kurikulum bagi memastikan budaya inovasi sentiasa
menjadi amalan dalam kalangan guru demi mengangkat profesionalisme guru di
Malaysia
Fair Exchange in Strand Spaces
Many cryptographic protocols are intended to coordinate state changes among
principals. Exchange protocols coordinate delivery of new values to the
participants, e.g. additions to the set of values they possess. An exchange
protocol is fair if it ensures that delivery of new values is balanced: If one
participant obtains a new possession via the protocol, then all other
participants will, too. Fair exchange requires progress assumptions, unlike
some other protocol properties. The strand space model is a framework for
design and verification of cryptographic protocols. A strand is a local
behavior of a single principal in a single session of a protocol. A bundle is a
partially ordered global execution built from protocol strands and adversary
activities. The strand space model needs two additions for fair exchange
protocols. First, we regard the state as a multiset of facts, and we allow
strands to cause changes in this state via multiset rewriting. Second, progress
assumptions stipulate that some channels are resilient-and guaranteed to
deliver messages-and some principals are assumed not to stop at certain
critical steps. This method leads to proofs of correctness that cleanly
separate protocol properties, such as authentication and confidentiality, from
invariants governing state evolution. G. Wang's recent fair exchange protocol
illustrates the approach
Coherent exciton-vibrational dynamics and energy transfer in conjugated organics
Coherence, signifying concurrent electron-vibrational dynamics in complex natural and man-made systems, is currently a subject of intense study. Understanding this phenomenon is important when designing carrier transport in optoelectronic materials. Here, excited state dynamics simulations reveal a ubiquitous pattern in the evolution of photoexcitations for a broad range of molecular systems. Symmetries of the wavefunctions define a specific form of the non-adiabatic coupling that drives quantum transitions between excited states, leading to a collective asymmetric vibrational excitation coupled to the electronic system. This promotes periodic oscillatory evolution of the wavefunctions, preserving specific phase and amplitude relations across the ensemble of trajectories. The simple model proposed here explains the appearance of coherent exciton-vibrational dynamics due to non-adiabatic transitions, which is universal across multiple molecular systems. The observed relationships between electronic wavefunctions and the resulting functionalities allows us to understand, and potentially manipulate, excited state dynamics and energy transfer in molecular materials.Fil: Nelson, Tammie R.. Los Alamos National Laboratory; Estados UnidosFil: Ondarse Alvarez, Dianelys. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes; ArgentinaFil: Oldani, Andres Nicolas. Universidad Nacional de Quilmes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Rodríguez Hernández, Beatriz. Universidad Nacional de Quilmes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Alfonso Hernandez, Laura. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes; ArgentinaFil: Galindo, Johan F.. Universidad Nacional de Colombia; ColombiaFil: Kleiman, Valeria D.. University of Florida; Estados UnidosFil: Fernández Alberti, Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes; ArgentinaFil: Roitberg, Adrián. University of Florida; Estados UnidosFil: Tretiak, Sergei. Los Alamos National Laboratory; Estados Unido
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