11,322 research outputs found
A proposal for founding mistrustful quantum cryptography on coin tossing
A significant branch of classical cryptography deals with the problems which
arise when mistrustful parties need to generate, process or exchange
information. As Kilian showed a while ago, mistrustful classical cryptography
can be founded on a single protocol, oblivious transfer, from which general
secure multi-party computations can be built.
The scope of mistrustful quantum cryptography is limited by no-go theorems,
which rule out, inter alia, unconditionally secure quantum protocols for
oblivious transfer or general secure two-party computations. These theorems
apply even to protocols which take relativistic signalling constraints into
account. The best that can be hoped for, in general, are quantum protocols
computationally secure against quantum attack. I describe here a method for
building a classically certified bit commitment, and hence every other
mistrustful cryptographic task, from a secure coin tossing protocol. No
security proof is attempted, but I sketch reasons why these protocols might
resist quantum computational attack.Comment: Title altered in deference to Physical Review's fear of question
marks. Published version; references update
Atmospheric Backscatter Model Development for CO Sub 2 Wavelengths
The results of investigations into the problems of modeling atmospheric backscatter from aerosols, in the lowest 20 km of the atmosphere, at CO2 wavelengths are presented, along with a summary of the relevant aerosol characteristics and their variability, and a discussion of the measurement techniques and errors involved. The different methods of calculating the aerosol backscattering function, both from measured aerosol characteristics and from optical measurements made at other wavelengths, are discussed in detail, and limits are placed on the accuracy of these methods. The effects of changing atmospheric humidity and temperature on the backscatter are analyzed and related to the actual atmosphere. Finally, the results of modeling CO2 backscatter in the atmosphere are presented and the variation with height and geographic location discussed, and limits placed on the magnitude of the backscattering function. Conclusions regarding modeling techniques and modeled atmospheric backscatter values are presented in tabular form
Coin Tossing is Strictly Weaker Than Bit Commitment
We define cryptographic assumptions applicable to two mistrustful parties who
each control two or more separate secure sites between which special relativity
guarantees a time lapse in communication. We show that, under these
assumptions, unconditionally secure coin tossing can be carried out by
exchanges of classical information. We show also, following Mayers, Lo and
Chau, that unconditionally secure bit commitment cannot be carried out by
finitely many exchanges of classical or quantum information. Finally we show
that, under standard cryptographic assumptions, coin tossing is strictly weaker
than bit commitment. That is, no secure classical or quantum bit commitment
protocol can be built from a finite number of invocations of a secure coin
tossing black box together with finitely many additional information exchanges.Comment: Final version; to appear in Phys. Rev. Let
Effects of Domain Wall on Electronic Transport Properties in Mesoscopic Wire of Metallic Ferromagnets
We study the effect of the domain wall on electronic transport properties in
wire of ferromagnetic 3 transition metals based on the linear response
theory. We considered the exchange interaction between the conduction electron
and the magnetization, taking into account the scattering by impurities as
well. The effective electron-wall interaction is derived by use of a local
gauge transformation in the spin space. This interaction is treated
perturbatively to the second order. The conductivity contribution within the
classical (Boltzmann) transport theory turns out to be negligiblly small in
bulk magnets, due to a large thickness of the wall compared with the fermi
wavelength. It can be, however, significant in ballistic nanocontacts, as
indicated in recent experiments. We also discuss the quantum correction in
disordered case where the quantum coherence among electrons becomes important.
In such case of weak localization the wall can contribute to a decrease of
resistivity by causing dephasing. At lower temperature this effect grows and
can win over the classical contribution, in particular in wire of diameter
, being the inelastic diffusion
length. Conductance change of the quantum origin caused by the motion of the
wall is also discussed.Comment: 30 pages, 4 figures. Detailed paper of Phys. Rev. Lett. 78, 3773
(1997). Submitted to J. Phys. Soc. Jp
Expression in Escherichia coli of a cloned DNA sequence encoding the pre-S2 region of hepatitis B virus
A DNA sequence encoding the entire pre-S2 region (amino acids 120-174; serotype ayw) of human hepatitis B virus envelope protein has been inserted into the lacZ gene of the plasmid pSKS105 yielding a recombinant, pWS3. Lac+ colonies of the Escherichia coli M182 (lacIOPZYA), isolated after transformation with pWS3, produced a pre-S2 peptide-ß-galactosidase fusion protein. This fusion protein, which comprised as much as 3% of the total bacterial protein, was purified to >90% homogeneity by affinity chromatography on p-aminophenyl-ß-D-thiogalactoside-Sepharose. It is immunoprecipitable with rabbit antibodies to a synthetic peptide corresponding to amino acids 120-145 of the pre-S2 region of serotype adw [pre-S(120-145)] or with antibodies to hepatitis B virus. pre-S(120-145) completely blocked the binding of either antibody to the pre-S2 peptide-ß-galactosidase fusion protein. These results indicate that there are antigenic determinants on the fusion protein that are closely related to, if not identical to, determinants on synthetic pre-S(120-145) and on pre-S2 sequences of native hepatitis B virus particles. Thus, bacteria transformed with pWS3 can provide an abundant source of pre-S2-ß-galactosidase fusion protein, which may prove useful either as a diagnostic reagent possessing marker enzyme activity suitable for ELISA tests or as an immunogen with potential to contribute to active prophylaxis of hepatitis B
Are Newly Discovered HI High Velocity Clouds Minihalos in the Local Group?
A set of HI sources extracted from the north Galactic polar region by the
ongoing ALFALFA survey has properties that are consistent with the
interpretation that they are associated with isolated minihalos in the
outskirts of the Local Group (LG). Unlike objects detected by previous surveys,
such as the Compact High Velocity Clouds of Braun & Burton (1999), the HI
clouds found by ALFALFA do not violate any structural requirements or halo
scaling laws of the LambdaCDM structure paradigm, nor would they have been
detected by extant HI surveys of nearby galaxy groups other than the LG. At a
distance of d Mpc, their HI masses range between $5 x 10^4 d^2 and 10^6 d^2
solar and their HI radii between <0.4d and 1.6 d kpc. If they are parts of
gravitationally bound halos, the total masses would be on order of 10^8--10^9
solar, their baryonic content would be signifcantly smaller than the cosmic
fraction of 0.16 and present in a ionized gas phase of mass well exceeding that
of the neutral phase. This study does not however prove that the minihalo
interpretation is unique. Among possible alternatives would be that the clouds
are shreds of the Leading Arm of the Magellanic Stream.Comment: 4 pages, 3 figures, 1 table; to appear Ap.J. Letter
Magnetization and EPR studies of the single molecule magnet Ni with integrated sensors
Integrated magnetic sensors that allow simultaneous EPR and magnetization
measurements have been developed to study single molecule magnets. A high
frequency microstrip resonator has been integrated with a micro-Hall effect
magnetometer. EPR spectroscopy is used to determine the energy splitting
between the low lying spin-states of a Ni single crystal, with an S=4
ground state, as a function of applied fields, both longitudinal and transverse
to the easy axis at 0.4 K. Concurrent magnetization measurements show changes
in spin-population associated with microwave absorption. Such studies enable
determination of the energy relaxation time of the spin system.Comment: 4 pages, 4 figures, accepted for publication (Proceedings of the 10th
Joint MMM/Intermag Conference, which will be published as special issues of
the Journal of Applied Physics
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