18,785 research outputs found
Clocking connector replaces adapter cables
Single cable using simplified, versatile clocking connector satisfies clocking variations that previously required many cables. Connector consists of specially fabricated grommet follower dial housing, dial assembly, and modified insert
Real sequence effects on the search dynamics of transcription factors on DNA
Recent experiments show that transcription factors (TFs) indeed use the
facilitated diffusion mechanism to locate their target sequences on DNA in
living bacteria cells: TFs alternate between sliding motion along DNA and
relocation events through the cytoplasm. From simulations and theoretical
analysis we study the TF-sliding motion for a large section of the DNA-sequence
of a common E. coli strain, based on the two-state TF-model with a fast-sliding
search state and a recognition state enabling target detection. For the
probability to detect the target before dissociating from DNA the TF-search
times self-consistently depend heavily on whether or not an auxiliary operator
(an accessible sequence similar to the main operator) is present in the genome
section. Importantly, within our model the extent to which the interconversion
rates between search and recognition states depend on the underlying nucleotide
sequence is varied. A moderate dependence maximises the capability to
distinguish between the main operator and similar sequences. Moreover, these
auxiliary operators serve as starting points for DNA looping with the main
operator, yielding a spectrum of target detection times spanning several orders
of magnitude. Auxiliary operators are shown to act as funnels facilitating
target detection by TFs.Comment: 26 pages, 7 figure
Discrete Nonlinear Schr{\"o}dinger Breathers in a Phonon Bath
We study the dynamics of the discrete nonlinear Schr{\"o}dinger lattice
initialized such that a very long transitory period of time in which standard
Boltzmann statistics is insufficient is reached. Our study of the nonlinear
system locked in this {\em non-Gibbsian} state focuses on the dynamics of
discrete breathers (also called intrinsic localized modes). It is found that
part of the energy spontaneously condenses into several discrete breathers.
Although these discrete breathers are extremely long lived, their total number
is found to decrease as the evolution progresses. Even though the total number
of discrete breathers decreases we report the surprising observation that the
energy content in the discrete breather population increases. We interpret
these observations in the perspective of discrete breather creation and
annihilation and find that the death of a discrete breather cause effective
energy transfer to a spatially nearby discrete breather. It is found that the
concepts of a multi-frequency discrete breather and of internal modes is
crucial for this process. Finally, we find that the existence of a discrete
breather tends to soften the lattice in its immediate neighborhood, resulting
in high amplitude thermal fluctuation close to an existing discrete breather.
This in turn nucleates discrete breather creation close to a already existing
discrete breather
Realizing time crystals in discrete quantum few-body systems
The exotic phenomenon of time translation symmetry breaking under periodic
driving - the time crystal - has been shown to occur in many-body systems even
in clean setups where disorder is absent. In this work, we propose the
realization of time-crystals in few-body systems, both in the context of
trapped cold atoms with strong interactions and of a circuit of superconducting
qubits. We show how these two models can be treated in a fairly similar way by
adopting an effective spin chain description, to which we apply a simple
driving protocol. We focus on the response of the magnetization in the presence
of imperfect pulses and interactions, and show how the results can be
interpreted, in the cold atomic case, in the context of experiments with
trapped bosons and fermions. Furthermore, we provide a set of realistic
parameters for the implementation of the superconducting circuit.Comment: 6 pages, 4 figure
Note on SLE and logarithmic CFT
It is discussed how stochastic evolutions may be linked to logarithmic
conformal field theory. This introduces an extension of the stochastic Loewner
evolutions. Based on the existence of a logarithmic null vector in an
indecomposable highest-weight module of the Virasoro algebra, the
representation theory of the logarithmic conformal field theory is related to
entities conserved in mean under the stochastic process.Comment: 10 pages, LaTeX, v2: version to be publishe
First results of the XI Groups Project: Studying an unbiased sample of galaxy groups
X-ray observations of hot, intergalactic gas in galaxy groups provide a
useful means of characterizing the global properties of groups. However, X-ray
studies of large group samples have typically involved very shallow X-ray
exposures or have been based on rather heterogeneous samples. Here we present
the first results of the XI (XMM/IMACS) Groups Project, a study targeting, for
the first time, a redshift-selected, statistically unbiased sample of galaxy
groups using deep X-ray data. Combining this with radio observations of cold
gas and optical imaging and spectroscopy of the galaxy population, the project
aims to advance the understanding of how the properties and dynamics of group
galaxies relate to global group properties. Here, X-ray and optical data of the
first four galaxy groups observed as part of the project are presented. In two
of the groups we detect diffuse emission with a luminosity of L_X ~ 10^41
erg/s, among the lowest found for any X-ray detected group thus far, with a
comparable upper limit for the other two. Compared to typical X-ray selected
groups of similar velocity dispersion, these four systems are all surprisingly
X-ray faint. We discuss possible explanations for the lack of significant X-ray
emission in the groups, concluding that these systems are most likely
collapsing for the first time. Our results strongly suggest that, unlike our
current optically selected sample, previous X-ray selected group samples
represented a biased picture of the group population. This underlines the
necessity of a study of this kind, if one is to reach an unbiased census of the
properties of galaxy groups and the distribution of baryons in the Universe.Comment: 14 pages, 8 figures, accepted for publication in MNRA
Intrinsic localized modes in the charge-transfer solid PtCl
We report a theoretical analysis of intrinsic localized modes in a
quasi-one-dimensional charge-transfer-solid (PtCl). We discuss strongly nonlinear features of resonant Raman
overtone scattering measurements on PtCl, arising from quantum intrinsic
localized (multiphonon) modes (ILMs) and ILM-plus-phonon states. We show, that
Raman scattering data displays clear signs of a non-thermalization of lattice
degrees-of-freedom, manifested in a nonequilibrium density of intrinsic
localized modes.Comment: 4 pages, 4 figures, REVTE
Defect Tolerant Monolayer Transition Metal Dichalcogenides
Localized electronic states formed inside the band gap of a semiconductor due
to crystal defects can be detrimental to the material's optoelectronic
properties. Semiconductors with lower tendency to form defect induced deep gap
states are termed defect tolerant. Here we provide a systematic first
principles investigation of defect tolerance in 29 monolayer transition metal
dichalcogenides (TMDs) of interest for nanoscale optoelectronics. We find that
the TMDs based on group VI and X metals form deep gap states upon creation of a
chalcogen (S, Se, Te) vacancy while the TMDs based on group IV metals form only
shallow defect levels and are thus predicted to be defect tolerant.
Interestingly, all the defect sensitive TMDs have valence and conduction bands
with very similar orbital composition. This indicates a bonding/anti-bonding
nature of the gap which in turn suggests that dangling bonds will fall inside
the gap. These ideas are made quantitative by introducing a descriptor that
measures the degree of similarity of the conduction and valence band manifolds.
Finally, the study is generalized to non-polar nanoribbons of the TMDs where we
find that only the defect sensitive materials form edge states within the band
gap
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