24,582 research outputs found
Effective pore size and radius of capture for K+ ions in K-channels
Indexación: Web of Science; Scopus.Reconciling protein functional data with crystal structure is arduous because rare conformations or crystallization artifacts occur. Here we present a tool to validate the dimensions of open pore structures of potassium-selective ion channels. We used freely available algorithms to calculate the molecular contour of the pore to determine the effective internal pore radius (r(E)) in several K-channel crystal structurss. r(E) was operationally defined as the radius of the biggest sphere able to enter the pore from the cytosolic side. We obtained consistent r(E) estimates for MthK and Kv1.2/2.1 structures, with r(E) = 5.3-5.9 angstrom and r(E) = 4.5-5.2 angstrom, respectively. We compared these structural estimates with functional assessments of the internal mouth radii of capture (r(C)) for two electrophysiological counterparts, the large conductance calcium activated K-channel (r(C) = 2.2 angstrom) and the Shaker K-v-channel (r(C) = 0.8 angstrom), for MthK and Kv1.2/2.1 structures, respectively. Calculating the difference between r(E) and r(C), produced consistent size radii of 3.1-3.7 angstrom and 3.6-4.4 angstrom for hydrated K+ ions. These hydrated K+ estimates harmonize with others obtained with diverse experimental and theoretical methods. Thus, these findings validate MthK and the Kv1.2/2.1 structures as templates for open BK and Kv-channels, respectively.http://recursosbiblioteca.unab.cl:2226/articles/srep1989
Detectors and Concepts for sub-100 ps timing with gaseous detectors
We give a short compendium of the main ongoing detectors and concepts capable
of performing accurate sub-100 ps timing at high particle fluxes and on large
areas, through technologies based on gaseous media. We briefly discuss the
state-of-the-art, technological limitations and prospects, and a new bizarre
idea
Coupled channel study of photoproduction
A coupled channel model with , and channels has been
used to analyze the recent data of . The non-resonant
interactions within the subspace are derived from effective
Lagrangians using a unitary transformation method. The direct photoproduction
reaction is obtained from a chiral constituent quark model with breaking. Missing baryon resonances issues are briefly discussed.Comment: Part of the proceedings of the International Workshop on the Physics
of Excited Baryons NSTAR05, 12-15 October 2005, Tallahassee, Florida, US
The critical current of YBa2Cu3O7-d Low Angle Grain Boundaries
Transport critical current measurements have been performed on 5 degree
[001]-tilt thin film YBa2Cu3O7-delta single grain boundaries with magnetic
field rotated in the plane of the film, phi. The variation of the critical
current has been determined as a function of the angle between the magnetic
field and the grain boundary plane. In applied fields above 1 T the critical
current, j_c, is found to be strongly suppressed only when the magnetic field
is within an angle phi_k of the grain boundary. Outside this angular range the
behavior of the artificial grain boundary is dominated by the critical current
of the grains. We show that the phi dependence of j_c in the suppressed region
is well described by a flux cutting model.Comment: To be published in PRL, new version with minor changes following
referees report
Complex joint probabilities as expressions of determinism in quantum mechanics
The density operator of a quantum state can be represented as a complex joint
probability of any two observables whose eigenstates have non-zero mutual
overlap. Transformations to a new basis set are then expressed in terms of
complex conditional probabilities that describe the fundamental relation
between precise statements about the three different observables. Since such
transformations merely change the representation of the quantum state, these
conditional probabilities provide a state-independent definition of the
deterministic relation between the outcomes of different quantum measurements.
In this paper, it is shown how classical reality emerges as an approximation to
the fundamental laws of quantum determinism expressed by complex conditional
probabilities. The quantum mechanical origin of phase spaces and trajectories
is identified and implications for the interpretation of quantum measurements
are considered. It is argued that the transformation laws of quantum
determinism provide a fundamental description of the measurement dependence of
empirical reality.Comment: 12 pages, including 1 figure, updated introduction includes
references to the historical background of complex joint probabilities and to
related work by Lars M. Johanse
Uncertainties in gas kinematics arising from stellar continuum modelling in integral field spectroscopy data: the case of NGC2906 observed with MUSE/VLT
We study how the use of several stellar subtraction methods and line fitting
approaches can affect the derivation of the main kinematic parameters (velocity
and velocity dispersion fields) of the ionized gas component. The target of
this work is the nearby galaxy NGC 2906, observed with the MUSE instrument at
Very Large Telescope. A sample of twelve spectra is selected from the inner
(nucleus) and outer (spiral arms) regions, characterized by different
ionization mechanisms. We compare three different methods to subtract the
stellar continuum (FIT3D, STARLIGHT and pPXF), combined with one of the
following stellar libraries: MILES, STELIB and GRANADA+MILES. The choice of the
stellar subtraction method is the most important ingredient affecting the
derivation of the gas kinematics, followed by the choice of the stellar library
and by the line fitting approach. In our data, typical uncertainties in the
observed wavelength and width of the H\alpha and [NII] lines are of the order
of _rms \sim 0.1\AA\ and _rms \sim 0.2\AA\ (\sim 5
and 10km/s, respectively). The results obtained from the [NII] line seem to be
slightly more robust, as it is less affected by stellar absorption than
H\alpha. All methods considered yield statistically consistent measurements
once a mean systemic contribution
\Delta\bar\lambda=\Delta\bar\sigma=0.2xDelta_{MUSE} is added in quadrature to
the line fitting errors, where \Delta_{MUSE} = 1.1\AA\ \sim 50 km/s denotes the
instrumental resolution of the MUSE spectra. Although the subtraction of the
stellar continuum is critical in order to recover line fluxes, any method
(including none) can be used in order to measure the gas kinematics, as long as
an additional component of 0.2 x Delta_MUSE is added to the error budget.Comment: 20 pages, 14 figure
Effect of the mechanical properties on drilling resistance of Al2O3-TiO2 coatings manufactured by atmospheric plasma spraying
Al2O3 with 13 and 45wt.% TiO2 microsized powders (6-22 and 13-41µm for each chemical composition) were used as raw materials to coat AISI 1040 steel by atmospheric plasma spraying. The mechanical properties of the coatings were measured by micro-indentation tests, and drilling experiments were carried out using high speed steel (HSS) rotary drill bits of various diameters and varying the load on the drill bits. In order to reduce the effect of the wear on the bit, a new bit was used for each test. According to the results, the drilling test is proposed as a method of determining the mechanical properties of these coatings from the correlation found between coating hardness and drilling resistance. © 2012 Elsevier B.V
Classical Novae as a Probe of the Cataclysmic Variable Population
Classical Novae (CNe) are the brightest manifestation of mass transfer onto a
white dwarf in a cataclysmic variable (CV). As such, they are probes of the
mass transfer rate, Mdot, and WD mass, Mwd, in these interacting binaries. Our
calculations of the dependence of the CN ignition mass, Mign, on Mdot and Mwd
yields the recurrence times of these explosions. We show that the observed CNe
orbital period distribution is consistent with the interrupted magnetic braking
evolutionary scenario, where at orbital periods Porb > 3 hr mass transfer is
driven by angular momentum loss via a wind from the companion star and at Porb
< 3 hr by gravitational radiation. About 50% of CNe occur in binaries accreting
at Mdot ~= 10^{-9} Msun/yr with Porb = 3-4 hr, with the remaining 50% split
evenly between Porb longer (higher Mdot) and shorter (lower Mdot) than this.
This resolution of the relative contribution to the CN rate from different CVs
tells us that 3(9)x10^5 CVs with WD mass 1.0(0.6)Msun are needed to produce one
CN per year. Using the K-band specific CN rate measured in external galaxies,
we find a CV birthrate of 2(4)x10^{-4}/yr per 10^{10}Lsun,K, very similar to
the luminosity specific Type Ia supernova rate in elliptical galaxies.
Likewise, we predict that there should be 60-180 CVs for every 10^6Lsun,K in an
old stellar population, similar to the number of X-ray identified CVs in the
globular cluster 47 Tuc, showing no overabundance relative to the field. Using
a two-component steady state model of CV evolution we show that the fraction of
CVs which are magnetic (22%) implies a birthrate of 8% relative to non-magnetic
CVs, similar to the fraction of strongly magnetic field WDs. (abridged)Comment: 6 pages, 2 figures, Accepted to the Astrophysical Journa
Exploring Halo Substructure with Giant Stars: Spectroscopy of Stars in the Galactic Anticenter Stellar Structure
To determine the nature of the recently discovered, ring-like stellar
structure at the Galactic anticenter, we have collected spectra of a set of
presumed constituent M giants selected from the 2MASS point source catalog.
Radial velocities have been obtained for stars spanning ~100 degrees,
exhibiting a trend in velocity with Galactic longitude and an estimated
dispersion of 20 +/- 4 km/sec. A mean metallicity [Fe/H] = -0.4 +/- 0.3
measured for these stars combines with previous evidence from the literature to
suggest a population with a significant metallicity spread. In addition, a
curious alignment of at least four globular clusters of lower mean metallicity
is noted to be spatially and kinematically consistent with this stellar
distribution. We interpret the M giant sample position and velocity variation
with Galactic longitude as suggestive of a satellite galaxy currently
undergoing tidal disruption in a non-circular, prograde orbit about the Milky
Way.Comment: (1) University of Virginia, 4 pages, 3 figures, accepted for
publication in The Astrophysical Journal Letter
Pengendalian Kualitas Proses Produksi Teh Hitam Di PT. Perkebunan Nusantara XII Unit Sirah Kencong
PT. Perkebunan Nusantara XII Unit Serah Kencong merupakan Perusahaan BUMN yang bergerak di bidang budidaya hasil perkebunan salah satunya teh hitam. Pengendalian kualitas yang dilakukan hanya berupa pencatatan hasil secara deskriptif sehingga hasilnya tidak mampu menunjukkan kebaikan suatu proses produksi. Pada Kenyataannya pabrik sering mengalami masalah pada volume density yang menyebabkan Perubahan kualitas dari rasa dan kepekatan warna. Density seringkali melebihi batas spesifikasi yang telah ditentukan yang membuat kualitas teh hitam menurun. Pada penelitian ini, pengendalian kualitas dilakukan secara multivariat karena density memberikan pengaruh terhadap karakteristik yang lain yaitu kepekatan warna dan rasa. Peta kendali yang digunakan adalah MEWMV dan MEWMA yang dinilai lebih sensitif terhadap pergeseran proses daripada peta kendali multivariat yang lainnya. Diperoleh hasil pembobot yang optimal adalah 0,9 untuk MEWMV dan MEWMA. Dari pembobot tersebut proses produksi teh hitam di PT. Perkebunan Nusantara XII Unit Serah Kencong XII belum terkendali secara statistik. Indeks kapabilitas multivariat yang diperoleh adalah sebesar 2,02. Sehingga ada kecenderungan kinerja proses telah kapabel pada ketiga variabel. Nilai yang diperoleh adalah -0,53 dimana nilai tersebut lebih kecil dari 1 sehingga kinerja proses multivariat belum kapabel
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