409 research outputs found
Mean-field methods in evolutionary duplication-innovation-loss models for the genome-level repertoire of protein domains
We present a combined mean-field and simulation approach to different models
describing the dynamics of classes formed by elements that can appear,
disappear or copy themselves. These models, related to a paradigm
duplication-innovation model known as Chinese Restaurant Process, are devised
to reproduce the scaling behavior observed in the genome-wide repertoire of
protein domains of all known species. In view of these data, we discuss the
qualitative and quantitative differences of the alternative model formulations,
focusing in particular on the roles of element loss and of the specificity of
empirical domain classes.Comment: 10 Figures, 2 Table
Radiative lifetime measurements of rubidium Rydberg states
We have measured the radiative lifetimes of ns, np and nd Rydberg states of
rubidium in the range 28 < n < 45. To enable long-lived states to be measured,
our experiment uses slow-moving Rb atoms in a magneto-optical trap (MOT). Two
experimental techniques have been adopted to reduce random and systematic
errors. First, a narrow-bandwidth pulsed laser is used to excite the target
Rydberg state, resulting in minimal shot-to-shot variation in the initial state
population. Second, we monitor the target state population as a function of
time delay from the laser pulse using a short-duration, millimetre-wave pulse
that is resonant with a one- or two-photon transition. We then selectively
field ionize the monitor state, and detect the resulting electrons with a
micro-channel plate. This signal is an accurate mirror of the target state
population, and is uncontaminated by contributions from other states which are
populated by black body radiation. Our results are generally consistent with
other recent experimental results obtained using a less sensitive method, and
are also in excellent agreement with theory.Comment: 27 pages,6 figure
Measurement of the electric dipole moments for transitions to rubidium Rydberg states via Autler-Townes splitting
We present the direct measurements of electric-dipole moments for
transitions with for Rubidium atoms. The
measurements were performed in an ultracold sample via observation of the
Autler-Townes splitting in a three-level ladder scheme, commonly used for
2-photon excitation of Rydberg states. To the best of our knowledge, this is
the first systematic measurement of the electric dipole moments for transitions
from low excited states of rubidium to Rydberg states. Due to its simplicity
and versatility, this method can be easily extended to other transitions and
other atomic species with little constraints. Good agreement of the
experimental results with theory proves the reliability of the measurement
method.Comment: 12 pages, 6 figures; figure 6 replaced with correct versio
Robust Myco-Composites as a Platform for Versatile Hybrid-Living Structural Materials
Fungal mycelium, a living network of filamentous threads, thrives on
lignocellulosic waste and exhibits rapid growth, hydrophobicity, and intrinsic
regeneration, offering a potential means to create next-generation sustainable
and functional composites. However, existing hybrid-living mycelium composites
(myco-composites) are tremendously constrained by conventional mold-based
manufacturing processes, which are only compatible with simple geometries and
coarse biomass substrates that enable gas exchange. Here we introduce a class
of structural myco-composites manufactured with a novel platform that harnesses
high-resolution biocomposite additive manufacturing and robust mycelium
colonization with indirect inoculation. We leverage principles of hierarchical
composite design and selective nutritional provision to create a robust
myco-composite that is scalable, tunable, and compatible with complex
geometries. To illustrate the versatility of this platform, we characterize the
impact of mycelium colonization on mechanical and surface properties of the
composite, finding that it yields the strongest mycelium composite reported to
date, and demonstrate fabrication of unique foldable bio-welded containers and
flexible mycelium textiles. This study bridges the gap between biocomposite and
hybrid-living materials research, opening the door to advanced structural
mycelium applications and demonstrating a novel platform for development of
diverse hybrid-living materials
Effect of photoions on the line shapes of the F\"orster resonance and microwave transitions in cold rubidium Rydberg atoms
Experiments on the spectroscopy of the F\"orster resonance Rb(37P)+Rb(37P) ->
Rb(37S)+Rb(38S) and microwave transitions nP -> n'S, n'D between Rydberg states
of cold Rb atoms in a magneto-optical trap have been performed. Under ordinary
conditions, all spectra exhibited a 2-3 MHz line width independently of the
interaction time of atoms with each other or with microwave radiation, although
the ultimate resonance width should be defined by the inverse interaction time.
Analysis of the experimental conditions has shown that the main source of the
line broadening was the inhomogeneous electric field of cold photoions appeared
at the excitation of initial Rydberg nP states by broadband pulsed laser
radiation. Using an additional pulse of the electric field, which rapidly
removed the photoions after the laser pulse, lead to a substantial narrowing of
the microwave and F\"orster resonances. An analysis of various sources of the
line broadening in cold Rydberg atoms has been conducted.Comment: 10 pages, 6 figure
Statistical Mechanics of Membrane Protein Conformation: A Homopolymer Model
The conformation and the phase diagram of a membrane protein are investigated
via grand canonical ensemble approach using a homopolymer model. We discuss the
nature and pathway of -helix integration into the membrane that results
depending upon membrane permeability and polymer adsorptivity. For a membrane
with the permeability larger than a critical value, the integration becomes the
second order transition that occurs at the same temperature as that of the
adsorption transition. For a nonadsorbing membrane, the integration is of the
first order due to the aggregation of -helices.Comment: RevTeX with 5 postscript figure
Application of the Multi-modal Relevance Vector Machine to the Problem of Protein Secondary Structure Prediction
The aim of the paper is to experimentally examine the plausibility of Relevance Vector Machines (RVM) for protein secondary structure prediction. We restrict our attention to detecting strands which represent an especially problematic element of the secondary structure. The commonly adopted local principle of secondary structure prediction is applied, which implies comparison of a sliding window in the given polypeptide chain with a number of reference amino-acid sequences cut out of the training proteins as benchmarks representing the classes of secondary structure. As distinct from the classical RVM, the novel version applied in this paper allows for selective combination of several tentative window comparison modalities. Experiments on the RS126 data set have shown its ability to essentially decrease the number of reference fragments in the resulting decision rule and to select a subset of the most appropriate comparison modalities within the given set of the tentative ones. © 2012 Springer-Verlag
Energetic Components of Cooperative Protein Folding
A new lattice protein model with a four-helix bundle ground state is analyzed
by a parameter-space Monte Carlo histogram technique to evaluate the effects of
an extensive variety of model potentials on folding thermodynamics. Cooperative
helical formation and contact energies based on a 5-letter alphabet are found
to be insufficient to satisfy calorimetric and other experimental criteria for
two-state folding. Such proteinlike behaviors are predicted, however, by models
with polypeptide-like local conformational restrictions and
environment-dependent hydrogen bonding-like interactions.Comment: 11 pages, 4 postscripts figures, Phys. Rev. Lett. (in press
Composite structural motifs of binding sites for delineating biological functions of proteins
Most biological processes are described as a series of interactions between
proteins and other molecules, and interactions are in turn described in terms
of atomic structures. To annotate protein functions as sets of interaction
states at atomic resolution, and thereby to better understand the relation
between protein interactions and biological functions, we conducted exhaustive
all-against-all atomic structure comparisons of all known binding sites for
ligands including small molecules, proteins and nucleic acids, and identified
recurring elementary motifs. By integrating the elementary motifs associated
with each subunit, we defined composite motifs which represent
context-dependent combinations of elementary motifs. It is demonstrated that
function similarity can be better inferred from composite motif similarity
compared to the similarity of protein sequences or of individual binding sites.
By integrating the composite motifs associated with each protein function, we
define meta-composite motifs each of which is regarded as a time-independent
diagrammatic representation of a biological process. It is shown that
meta-composite motifs provide richer annotations of biological processes than
sequence clusters. The present results serve as a basis for bridging atomic
structures to higher-order biological phenomena by classification and
integration of binding site structures.Comment: 34 pages, 7 figure
Searching for New Physics beyond the Standard Model in Electric Dipole Moment
This is a theoretical review of exploration of new physics beyond the
Standard Model (SM) in electric dipole moment (EDM) in elementary particles,
atoms, and molecule. EDM is a very important CP violating phenomenon and
sensitive to new physics. Starting with the estimations of EDM of
quarks-leptons in the SM, we explore the new signals beyond the SM. However,
these works drive us to more wide fronteers where we serach fundamental physics
using atoms and molecules and vice versa. Paramagnetic atoms and molecules have
great enhancement factor on electron EDM. Diamagnetic atoms and molecules are
very sensitive to nuclear P and T odd processes. Thus the EDM becomes the key
word not only of New Physics but also of unprecedented fruitful collaboration
among particle, atomic. molecular physics. This review intends to help such
collaboration over the wide range of physicists.Comment: 95pages. References are added. Appendix K is revise
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