30,391 research outputs found
A study of copper and copper proteins in the eggs of <i>Sepia officinalis</i> L.
1. Eggs from Sepia officinalis L. contain a high amount of copper (109 fxg/g dry weight ). The water soluble extracts of these eggs have been studied. The copper content of the extracts at different pH-values were determined with an atomic absorption spectrophotometer and with the bathocuproin sulphonate method. The proteins in the different extracts were studied by electrophoretic techniques.2. The extracted egg proteins were difficult to handle. They have a high molecular weight and show no migration after electrophoresis in 6 % acrylamide gels.3. Fragmentation of the extracted egg proteins has been effectuated by enzymatic treatment followed by the addition of 8M uruem, and by alkaline hydrolysis. Only the latter procedure resulted in electrophoretically migrating copper containing protein fragments.4. After SDS electrophoresis of the copper containing protein fragments, relative molecular masses (Mr) of 3800, 8600, 17800, 35300 and 132000 were observed
A Miniature Robot for Isolating and Tracking Neurons in Extracellular Cortical Recordings
This paper presents a miniature robot device and control algorithm that can autonomously position electrodes in cortical tissue for isolation and tracking of extracellular signals of individual neurons. Autonomous electrode positioning can significantly enhance the efficiency and quality of acute electrophysiolgical experiments aimed at basic understanding of the nervous system. Future miniaturized systems of this sort could also overcome some of the inherent difficulties in estabilishing long-lasting neural interfaces that are needed for practical realization of neural prostheses. The paper describes the robot's design and summarizes the overall structure of the control system that governs the electrode positioning process. We present a new sequential clustering algorithm that is key to improving our system's performance, and which may have other applications in robotics. Experimental results in macaque cortex demonstrate the validity of our approach
Navigation in Curved Space-Time
A covariant and invariant theory of navigation in curved space-time with
respect to electromagnetic beacons is written in terms of J. L. Synge's
two-point invariant world function. Explicit equations are given for navigation
in space-time in the vicinity of the Earth in Schwarzschild coordinates and in
rotating coordinates. The restricted problem of determining an observer's
coordinate time when their spatial position is known is also considered
Probing nuclear expansion dynamics with -spectra
We study the dynamics of charged pions in the nuclear medium via the ratio of
differential - and -spectra in a coupled-channel BUU (CBUU)
approach. The relative energy shift of the charged pions is found to correlate
with the pion freeze-out time in nucleus-nucleus collisions as well as with the
impact parameter of the heavy-ion reaction. Furthermore, the long-range Coulomb
force provides a 'clock' for the expansion of the hot nuclear system. Detailed
comparisons with experimental data for at 1 GeV/A and at
2.0 GeV/A are presented.Comment: 21 pages, latex, figures include
Teaching Species
A clear understanding of the term species is fundamental to the subject of evolution. However, introductory textbooks often fail to address this topic until one of the later chapters, after having used the term species in all preceding chapters. Furthermore, definitions of terms critical to a clear understanding of this subject are often vague or absent in chapters on species concepts. We feel the popular notion of a species problem has been unnecessarily inflated by this less-than-effective educational approach. Clearly addressing this essential subject at the beginning of a course on evolution will prepare students to learn the details and complexities of evolution. Here we provide the background for an alternative approach to this foundational topic, followed by an outlined lesson plan. We emphasize early introduction of this subject in texts and courses using unambiguous terminology and including the historical development of species concepts
A catalogue of the Chandra Deep Field South with multi-colour classification and photometric redshifts from COMBO-17
We present the COMBO-17 object catalogue of the Chandra Deep Field South for
public use, covering a field which is 31.5' x 30' in size. This catalogue lists
astrometry, photometry in 17 passbands from 350 to 930 nm, and ground-based
morphological data for 63,501 objects. The catalogue also contains multi-colour
classification into the categories 'Star', 'Galaxy' and 'Quasar' as well as
photometric redshifts. We include restframe luminosities in Johnson, SDSS and
Bessell passbands and estimated errors. The redshifts are most reliable at
R<24, where the sample contains approximately 100 quasars, 1000 stars and 10000
galaxies. We use nearly 1000 spectroscopically identified objects in
conjunction with detailed simulations to characterize the performance of
COMBO-17. We show that the selection of quasars, more generally type-1 AGN, is
nearly complete and minimally contaminated at z=[0.5,5] for luminosities above
M_B=-21.7. Their photometric redshifts are accurate to roughly 5000 km/sec.
Galaxy redshifts are accurate to 1% in dz/(1+z) at R<21. They degrade in
quality for progressively fainter galaxies, reaching accuracies of 2% for
galaxies with R~222 and of 10% for galaxies with R>24. The selection of stars
is complete to R~23, and deeper for M stars. We also present an updated
discussion of our classification technique with maps of survey completeness,
and discuss possible failures of the statistical classification in the faint
regime at R>24.Comment: submitted to Astronomy & Astrophysics, public data set available at
http://www.mpia.de/COMBO/combo_index.htm
Non-perturbative effects in semi-leptonic B_c decays
We discuss the impact of the soft degrees of freedom inside the B_c meson on
its rate in the semi-leptonic decay B_c -> X l nu_l where X denotes light
hadrons below the D^0 threshold. In particular we identify contributions
involving soft hadrons which are non-vanishing in the limit of massless
leptons. These contributions become relevant for a measurement of the purely
leptonic B_c decay rate, which due to helicity suppression involves a factor
m_l^2 and thus is much smaller than the contributions involving soft hadrons.Comment: LaTeX, 22 pages, 1 figur
Atomic states in optical traps near a planar surface
In this work we discuss the atomic states in a vertical optical lattice in
proximity of a surface. We study the modifications to the ordinary
Wannier-Stark states in presence of a surface and we characterize the energy
shifts produced by the Casimir-Polder interaction between atom and mirror. In
this context, we introduce an effective model describing the finite size of the
atom in order to regularize the energy corrections. In addition, the
modifications to the energy levels due to a hypothetical non-Newtonian
gravitational potential as well as their experimental observability are
investigated.Comment: 12 pages, 8 figure
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