1,433 research outputs found
The Aladin2 experiment: status and perspectives
Aladin2 is an experiment devoted to the first measurement of variations of
Casimir energy in a rigid cavity. The main scientific motivation relies on the
possibility of the first demonstration of a phase transition influenced by
vacuum fluctuations. The guiding principle of the measurement, based on the
behaviour of the critical field for an in-cavity superconducting film, will be
only briefly recalled. In this paper, after an introduction to the long term
motivations, the experimental apparatus and the results of the first
measurement of sensitivity will be presented in detail, particularly in
comparison with the expected signal. Last, the most important steps towards the
final measurement will be discussed.Comment: Talk given by Calloni at QFEXT05 Conference in Barcelona: Quantum
Field Theory Under the Influence of External Condition
The regions of the sequence most exposed to the solvent within the amyloidogenic state of a protein initiate the aggregation process.
Formation of misfolded aggregates is an essential part of what proteins can do. The process of protein aggregation is central to many human diseases and any aggregating event needs to be prevented within a cell and in protein design. In order to aggregate, a protein needs to unfold its native state, at least partially. The conformational state that is prone to aggregate is difficult to study, due to its aggregating potential and heterogeneous nature. Here, we use a systematic approach of limited proteolysis, in combination with electrospray ionisation mass spectrometry, to investigate the regions that are most flexible and solvent-exposed within the native, ligand-bound and amyloidogenic states of muscle acylphosphatase (AcP), a protein previously shown to form amyloid fibrils in the presence of trifluoroethanol. Seven proteases with different degrees of specificity have been used for this purpose. Following exposure to the aggregating conditions, a number of sites along the sequence of AcP become susceptible to proteolytic digestion. The pattern of proteolytic cleavages obtained under these conditions is considerably different from that of the native and ligand-bound conformations and includes a portion within the N-terminal tail of the protein (residues 6-7), the region of the sequence 18-23 and the position 94 near the C terminus. There is a significant overlap between the regions of the sequence found to be solvent-exposed from the present study and those previously identified to be critical in the rate-determining steps of aggregation from protein engineering approaches. This indicates that a considerable degree of solvent exposure is a feature of the portions of a protein that initiate the process of aggregation
Energy-momentum tensor for a Casimir apparatus in a weak gravitational field
The influence of the gravity acceleration on the regularized energy-momentum tensor of the quantized electromagnetic field between two plane parallel conducting plates is derived. We use Fermi coordinates and work to first order in the constant acceleration parameter. A perturbative expansion, to this order, of the Green functions involved and of the energy-momentum tensor is derived by means of the covariant geodesic point splitting procedure. In correspondence to the Green functions satisfying mixed and gauge-invariant boundary conditions, and Ward identities, the energy-momentum tensor is covariantly conserved and satisfies the expected relation between gauge-breaking and ghost parts, while a new simple formula for the trace anomaly is obtained to first order in the constant acceleration. A more systematic derivation is therefore obtained of the theoretical prediction according to which the Casimir device in a weak gravitational field will experience a tiny push in the upwards direction
Novel features of the energy momentum tensor of a Casimir apparatus in a weak gravitational field
The influence of the gravity acceleration on the regularized energy-momentum
tensor of the quantized electromagnetic field between two plane parallel
conducting plates is derived. A perturbative expansion, to first order in the
constant acceleration parameter, of the Green functions involved and of the
energy-momentum tensor is derived by means of the covariant geodesic point
splitting procedure. The energy-momentum tensor is covariantly conserved and
satisfies the expected relation between gauge-breaking and ghost parts.Comment: 8 pages, based on a talk given by Luigi Rosa at the QFEXT07
Conference, Leipzig. Equation (13) and the formulae for rho and energy E
stored in the Casimir device have been amended, jointly with related
discussio
Study of RPC gas mixtures for the ARGO-YBJ experiment
The ARGO-YBJ experiment consists of a RPC carpet to be operated at the
Yangbajing laboratory (Tibet, P.R. China), 4300 m a.s.l., and devoted to the
detection of showers initiated by photon primaries in the energy range 100 GeV
- 20 TeV. The measurement technique, namely the timing on the shower front with
a few tens of particles, requires RPC operation with 1 ns time resolution, low
strip multiplicity, high efficiency and low single counting rate. We have
tested RPCs with many gas mixtures, at sea level, in order to optimize these
parameters. The results of this study are reported.Comment: 6 pages, 3 figures. To be published in Nucl. Instr. Meth. A, talk
given at the "5th International Workshop on RPCs and Related Detectors", Bari
(Italy) 199
Relativistic mechanics of Casimir apparatuses in a weak gravitational field
This paper derives a set of general relativistic Cardinal Equations for the
equilibrium of an extended body in a uniform gravitational field. These
equations are essential for a proper understanding of the mechanics of
suspended relativistic systems. As an example, the prototypical case of a
suspended vessel filled with radiation is discussed. The mechanics of Casimir
apparatuses at rest in the gravitational field of the Earth is then considered.
Starting from an expression for the Casimir energy-momentum tensor in a weak
gravitational field recently derived by the authors, it is here shown that, in
the case of a rigid cavity supported by a stiff mount, the weight of the
Casimir energy stored in the cavity corresponds to a gravitational mass
, in agreement with the covariant conservation law of the
regularized energy-momentum tensor. The case of a cavity consisting of two
disconnected plates supported by separate mounts, where the two measured forces
cannot be obtained by straightforward arguments, is also discussed.Comment: 9 pages, improved presentation and new references adde
Vacuum fluctuation force on a rigid Casimir cavity in a gravitational field
We discuss the possibility of verifying the equivalence principle for the
zero-point energy of quantum electrodynamics, by evaluating the force, produced
by vacuum fluctuations, acting on a rigid Casimir cavity in a weak
gravitational field. The resulting force has opposite direction with respect to
the gravitational acceleration; the order of magnitude for a multi-layer cavity
configuration is derived and experimental feasibility is discussed, taking into
account current technological resources.Comment: 13 pages, Latex. In the revised version, the presentation has been
improve
Gravitational effects on a rigid Casimir cavity
Vacuum fluctuations produce a force acting on a rigid Casimir cavity in a
weak gravitational field. Such a force is here evaluated and is found to have
opposite direction with respect to the gravitational acceleration; the order of
magnitude for a multi-layer cavity configuration is analyzed and experimental
detection is discussed, bearing in mind the current technological resources.Comment: 7 pages, Latex. Talk given at the Fifth Leipzig Workshop on Quantum
Field Theory under the Influence of External Conditions, September 200
Casimir energy and the superconducting phase transition
We study the influence of Casimir energy on the critical field of a
superconducting film, and we show that by this means it might be possible to
directly measure, for the first time, the variation of Casimir energy that
accompanies the superconducting transition. It is shown that this novel
approach may also help clarifying the long-standing controversy on the
contribution of TE zero modes to the Casimir energy in real materials.Comment: 12 pages, 5 figures. Talk given at 7th Workshop on Quantum Field
Theory Under the Influence of External Conditions (QFEXT 05), Barcelona,
Catalonia, Spain, 5-9 Sep 200
BIOELECTROCHEMICAL SYSTEM FOR REMOVING HEXAVALENT CHROMIUM FROM WATERS
BES include a set of technologies that exploit the ability of certain microorganisms to use electrodes as the electrons acceptors/donors and to catalyze redox reactions in order to promote a flow of electrons. In the present study, we have assessed the possibility to remove Cr(VI) in a biocathodic chamber of a dual-chamber (2C) Microbial Electrolysis Cell (MEC) with cathode as the sole electron donor. The cathode was first put into the anodic compartment of a 2CMicrobial Fuel Cell (MFC) inoculated with sludge from an anaerobic digester. After the acclimation period, the electrode was transferred into the cathodic chamber to work at -300 mV (vs. Standard Hydrogen Electrode - SHE) as the biocathode in a Cr(VI)-reducing MEC with 2000 ÎĽg Cr(VI)/L. The acclimation phase in the 2C-MFC allowed to shorten the time for the electroactive-biofilm growth, and to increase the efficiency of the Cr(VI)-reducing MEC. The bioelectrochemical system ensured higher removal efficiency than the pure chemical process
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