25,306 research outputs found
Linking Stochastic Dynamics to Population Distribution: An Analytical Framework of Gene Expression
We present an analytical framework describing the steady-state distribution of protein concentration in live cells, considering that protein production occurs in random bursts with an exponentially distributed number of molecules. We extend this framework for cases of transcription autoregulation and noise propagation in a simple genetic network. This model allows for the extraction of kinetic parameters of gene expression from steady-state distributions of protein concentration in a cell population, which are available from single cell data obtained by flow cytometry or fluorescence microscopy
Direct frequency comb laser cooling and trapping
Continuous wave (CW) lasers are the enabling technology for producing
ultracold atoms and molecules through laser cooling and trapping. The resulting
pristine samples of slow moving particles are the de facto starting point for
both fundamental and applied science when a highly-controlled quantum system is
required. Laser cooled atoms have recently led to major advances in quantum
information, the search to understand dark energy, quantum chemistry, and
quantum sensors. However, CW laser technology currently limits laser cooling
and trapping to special types of elements that do not include highly abundant
and chemically relevant atoms such as hydrogen, carbon, oxygen, and nitrogen.
Here, we demonstrate that Doppler cooling and trapping by optical frequency
combs may provide a route to trapped, ultracold atoms whose spectra are not
amenable to CW lasers. We laser cool a gas of atoms by driving a two-photon
transition with an optical frequency comb, an efficient process to which every
comb tooth coherently contributes. We extend this technique to create a
magneto-optical trap (MOT), an electromagnetic beaker for accumulating the
laser-cooled atoms for further study. Our results suggest that the efficient
frequency conversion offered by optical frequency combs could provide a key
ingredient for producing trapped, ultracold samples of nature's most abundant
building blocks, as well as antihydrogen. As such, the techniques demonstrated
here may enable advances in fields as disparate as molecular biology and the
search for physics beyond the standard model.Comment: 10 pages, 5 figure
Practical Certificateless Aggregate Signatures From Bilinear Maps
Aggregate signature is a digital signature with a striking property that anyone can aggregate n individual signatures on n different messages which are signed by n distinct signers, into a single compact signature to reduce computational and storage costs. In this work, two practical certificateless aggregate signature schemes are proposed from bilinear maps. The first scheme CAS-1 reduces the costs of communication and signer-side computation but trades off the storage, while CAS-2 minimizes the storage but sacrifices the communication costs. One can choose either of the schemes by consideration of the application requirement. Compare with ID-based schemes, our schemes do not entail public key certificates as well and achieve the trust level 3, which imply the frauds of the authority are detectable. Both of the schemes are proven secure in the random oracle model by assuming the intractability of the computational Diffie-Hellman problem over the groups with bilinear maps, where the forking lemma technique is avoided
Anomalous scaling of conductivity in integrable fermion systems
We analyze the high-temperature conductivity in one-dimensional integrable
models of interacting fermions: the t-V model (anisotropic Heisenberg spin
chain) and the Hubbard model, at half-filling in the regime corresponding to
insulating ground state. A microcanonical Lanczos method study for finite size
systems reveals anomalously large finite-size effects at low frequencies while
a frequency-moment analysis indicates a finite d.c. conductivity. This
phenomenon also appears in a prototype integrable quantum system of
impenetrable particles, representing a strong-coupling limit of both models. In
the thermodynamic limit, the two results could converge to a finite d.c.
conductivity rather than an ideal conductor or insulator scenario.Comment: 6 pages, 3 figures. Submitted to PR
The Precise Formula in a Sine Function Form of the norm of the Amplitude and the Necessary and Sufficient Phase Condition for Any Quantum Algorithm with Arbitrary Phase Rotations
In this paper we derived the precise formula in a sine function form of the
norm of the amplitude in the desired state, and by means of he precise formula
we presented the necessary and sufficient phase condition for any quantum
algorithm with arbitrary phase rotations. We also showed that the phase
condition: identical rotation angles, is a sufficient but not a necessary phase
condition.Comment: 16 pages. Modified some English sentences and some proofs. Removed a
table. Corrected the formula for kol on page 10. No figure
Does afforestation deteriorate haze pollution in Beijing-Tianjin-Hebei (BTH), China?
Although aggressive emission control strategies have been implemented recently in the Beijing-Tianjin-Hebei area (BTH), China, pervasive and persistent haze still frequently engulfs the region during wintertime. Afforestation in BTH, primarily concentrated in the Taihang and Yan Mountains, has constituted one of the controversial factors exacerbating the haze pollution due to its slowdown of the surface wind speed. We report here an increasing trend of forest cover in BTH during 2001-2013 based on long-term satellite measurements and the impact of the afforestation on the fine-particle (PM2.5) level. Simulations using the Weather Research and Forecast model with chemistry reveal that afforestation in BTH since 2001 has generally been deteriorating the haze pollution in BTH to some degree, enhancing PM2.5 concentrations by up to 6% on average. Complete afforestation or deforestation in the Taihang and Yan Mountains would increase or decrease the PM2.5 level within 15% in BTH. Our model results also suggest that implementing a large ventilation corridor system would not be effective or beneficial to mitigate the haze pollution in Beijing
Mechanism of grain refinement of aluminium alloy in shear spinning under different deviation ratios
To investigate the grain refinement and its mechanism in shear spinning, microstructures of shear spun parts made by aluminium alloy under different deformation conditions, induced by different shear spinning deviation ratios, are studied. The results show that, after shear spinning, the microstructure is distributed symmetrically about a zone in sheet thickness defined as the neutral zone which is located between the inner surface and the middle plane of spun sheet thickness. Various deviation ratios in shear spinning can lead to grain refinement in different regions along thickness direction of the spun part. The microstructure characteristics indicate that the mechanism of grain refinement is due to the formation of deformation bands (DBs). It is observed that in DBs, parallel geometrically necessary boundaries (GNBs) formed by a zero deviation ratio and crossed GNBs formed by positive and negative deviation ratios are due to the different stress states induced by various deviation ratios in shear spinning. Due to the influence of grain refinement, micro hardness increases with the decreasing of the deviation ratio. The average value is increased by 16.04% under a negative deviation ratio compared to the initial micro hardness of the sheet
A key management architecture and protocols for secure smart grid communications
Providing encrypted communications among power grid components is expected to be a basic requirement of smart grid systems in the future. Here, we propose a key management architecture and associated protocols tailored to support encrypted smart grid communications. The architecture consists of two levels structured around the grid control system hierarchy. At the top level, which consist of control centers and regional coordinators, a bottom-up key structure is adopted using hash chaining and a logical key hierarchy. The lower level of the architecture consists of the regional coordinators (i.e., substations and distribution systems) and remote ends (e.g., meters and pole-top sensors) and utilizes a top-down key management approach built on an inverse element method. The proposed key management schema supports the hierarchical structure of the smart grid control mechanisms, and it takes the resource and electronic/physical security differences of the control levels into account. We define a set of protocols utilizing the architecture to provide secure unicast, multicast, and broadcast communications. Furthermore, we illustrate how the architecture is flexible enough to easily handle power grid nodes joining and leaving the system at the different levels. Lastly, we compare the proposed schema with existing ones and show that our architecture can achieve efficient key management to provide secure communications. Copyright © 2016 John Wiley & Sons, Ltd
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