129 research outputs found
Explaining the Unobserved: Why Quantum Theory Ain't Only About Information
A remarkable theorem by Clifton, Bub and Halvorson (2003) (CBH) characterizes quantum theory in terms of information--theoretic principles. According to Bub (2004, 2005) the philosophical significance of the theorem is that quantum theory should be regarded as a ``principle'' theory about (quantum) information rather than a ``constructive'' theory about the dynamics of quantum systems. Here we criticize Bub's principle approach arguing that if the mathematical formalism of quantum mechanics remains intact then there is no escape route from solving the measurement problem by constructive theories. We further propose a (Wigner--type) thought experiment that we argue demonstrates that quantum mechanics on the information--theoretic approach is incomplete
Dynamics of linear polymers in random media
We study phenomenological scaling theories of the polymer dynamics in random
media, employing the existing scaling theories of polymer chains and the
percolation statistics. We investigate both the Rouse and the Zimm model for
Brownian dynamics and estimate the diffusion constant of the center-of-mass of
the chain in such disordered media. For internal dynamics of the chain, we
estimate the dynamic exponents. We propose similar scaling theory for the
reptation dynamics of the chain in the framework of Flory theory for the
disordered medium. The modifications in the case of correlated disordered are
also discussed.Comment: 4 pages, no figure
Substrate recruitment mechanism by gram-negative type III, IV, and VI bacterial injectisomes
Bacteria use a wide arsenal of macromolecular substrates (DNA and proteins) to interact with or infect prokaryotic and eukaryotic cells. To do so, they utilize substrate-injecting secretion systems or injectisomes. However, prior to secretion, substrates must be recruited to specialized recruitment platforms and then handed over to the secretion apparatus for secretion. In this review, we provide an update on recent advances in substrate recruitment and delivery by gram-negative bacterial recruitment platforms associated with Type III, IV, and VI secretion systems
Revealing Cosmic Rotation
Cosmological Birefringence (CB), a rotation of the polarization plane of
radiation coming to us from distant astrophysical sources, may reveal parity
violation in either the electromagnetic or gravitational sectors of the
fundamental interactions in nature. Until only recently this phenomenon could
be probed with only radio observations or observations at UV wavelengths.
Recently, there is a substantial effort to constrain such non-standard models
using observations of the rotation of the polarization plane of cosmic
microwave background (CMB) radiation. This can be done via measurements of the
-modes of the CMB or by measuring its TB and EB correlations which vanish in
the standard model. In this paper we show that correlations-based
estimator is the best for upcoming polarization experiments. The based
estimator surpasses other estimators because it has the smallest noise and of
all the estimators is least affected by systematics. Current polarimeters are
optimized for the detection of -mode polarization from either primordial
gravitational waves or by large scale structure via gravitational lensing. In
the paper we also study optimization of CMB experiments for the detection of
cosmological birefringence, in the presence of instrumental systematics, which
by themselves are capable of producing correlations; potentially mimicking
CB.Comment: 10 pages, 3 figures, 2 table
Structural adaptation of a thermostable biotin-binding protein in a psychrophilic environment
Shwanavidin is an avidin-like protein from the marine proteobactrium Shewanella denitrificans, which exhibits an innate dimeric structure while maintaining high affinity toward biotin. A unique residue (Phe-43) from the L3,4 loop and a distinctive disulfide bridge were shown to account for the high affinity toward biotin. Phe-43 emulates the function and position of the critical intermonomeric Trp that characterizes the tetrameric avidins but is lacking in shwanavidin. The 18 copies of the apo-monomer revealed distinctive snapshots of L3,4 and Phe-43, providing rare insight into loop flexibility, binding site accessibility, and psychrophilic adaptation. Nevertheless, as in all avidins, shwanavidin also displays high thermostability properties. The unique features of shwanavidin may provide a platform for the design of a long sought after monovalent form of avidin, which would be ideal for novel types of biotechnological application
Position resolution and efficiency measurements with large scale Thin Gap Chambers for the super LHC
New developments in Thin Gap Chambers (TGC) detectors to provide fast trigger
and high precision muon tracking under sLHC conditions are presented. The
modified detectors are shown to stand a high total irradiation dose equivalent
to 6 Coulomb/cm of wire, without showing any deterioration in their
performance. Two large (1.2 x 0.8 m^2) prototypes containing four gaps, each
gap providing pad, strips and wires readout, with a total thickness of 50 mm,
have been constructed. Their local spatial resolution has been measured in a
100 GeV/c muon test beam at CERN. At perpendicular incidence angle, single gap
position resolution better than 60 microns has been obtained. For incidence
angle of 20 degrees resolution of less than 100 micron was achieved. TGC
prototypes were also tested under a flux of 10^5 Hz/cm^2 of 5.5-6.5 MeV
neutrons, showing a high efficiency for cosmic muons detection.Comment: Presented at the 12 Vienna conference on Instrumentation, February
201
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