7,604 research outputs found
Half-Heusler semiconductors as piezoelectrics
One of the central challenges in materials science is the design of
functional and multifunctional materials, in which large responses are produced
by applied fields and stresses. A rapidly developing paradigm for the rational
design of such materials is based on the first-principles study of a large
materials family, the perovskite oxides being the prototypical case.
Specifically, first-principles calculations of structure and properties are
used to explore the microscopic origins of the functional properties of
interest and to search a large space of equilibrium and metastable phases to
identify promising candidate systems. In this paper, we use a first-principles
rational-design approach to demonstrate semiconducting half-Heusler compounds
as a previously-unrecognized class of piezoelectric materials, and to provide
guidance for the experimental realization and further investigation of
high-performance materials suitable for practical applications.Comment: 5 pages, 3 figues, 3 table
Hexagonal as semiconducting ferroelectrics
We use a first-principles rational-design approach to identify a
previously-unrecognized class of ferroelectric materials in the LiGaGe
structure type. We calculate structural parameters, polarization and
ferroelectric well depths both for reported and as-yet hypothetical
representatives of this class. Our results provide guidance for the
experimental realization and further investigation of high-performance
materials suitable for practical applications.Comment: 5 pages, 2 figures, 3 table
Stochastic Gene Expression in Single Gene Oscillator Variants
It is infeasible to understand all dynamics in cell, but we can aim to understand the impact of design choices under our control. Here we consider a single gene oscillator as a case study to understand the influence of DNA copy number and repressor choice on the resulting dynamics. We first switch the repressor in the oscillator from the originally published lacI to treRL, a chimeric repressor with a lacI DNA binding domain that is inducible by trehalose. This slightly modified system produces faster and more regular oscillations than the original lacI oscillator. We then compare the treRL oscillator at three different DNA copy numbers. The period and amplitude of oscillations increases as the copy number is decreased. We cannot explain the change in period with differential equation models without changing delays or degradation rates. The correlation and phase coherence between daughter cells after cell division also tend to fall off faster for the lower copy oscillator variants. These results suggest that lower copy number variants of our single gene oscillator produce more synchronized oscillations
Stimulation of bioprocesses by ultrasound
Ultrasound (US) has become a ubiquitous technological process in a large variety of scientific disciplines. However, little information exists on the use of ultrasound to enhance biological processes and/or processing and consequently this paper provides an overview of work reported to date on this topic. This review provides a brief introduction to ultrasound and the history of ultrasound as applied to bioprocesses. This is followed by a discussion of the influence of US on discrete enzyme systems, enzymes used in bioremediation, microbial fermentations and enzymatic hydrolysis of biopolymers. Augmentation of anaerobic digestion by US is then considered along with enhancement of enzymes in food science and technology. The use of ultrasonically stimulated enzymes in synthesis is then considered and other relevant miscellaneous topics are described. It is concluded that the precise mechanism of action of US in bio-processing remains to be elucidated though a variety of plausible suggestions are made
Entanglement Swapping Chains for General Pure States
We consider entanglement swapping schemes with general (rather than
maximally) entangled bipartite states of arbitary dimension shared pairwise
between three or more parties in a chain. The intermediate parties perform
generalised Bell measurements with the result that the two end parties end up
sharing a entangled state which can be converted into maximally entangled
states. We obtain an expression for the average amount of maximal entanglement
concentrated in such a scheme and show that in a certain reasonably broad class
of cases this scheme is provably optimal and that, in these cases, the amount
of entanglement concentrated between the two ends is equal to that which could
be concentrated from the weakest link in the chain.Comment: 18 pages, 5 figure
Motion of the Zinc Ions in Catalysis by a Dizinc Metallo-β-Lactamase
We report rapid-freeze-quench X-ray absorption spectroscopy of a dizinc metallo-β-lactamase (MβL) reaction intermediate. The Zn(II) ions in the dinuclear active site of the S. maltophilia Class B3 MβL move away from each other, by ∼0.3 Å after 10 ms of reaction with nitrocefin, from 3.4 to 3.7 Å. Together with our previous characterization of the resting enzyme and its nitrocefin product complex, where the Zn(II) ion separation relaxes to 3.6 Å, these data indicate a scissoring motion of the active site that accompanies the ring-opening step. The average Zn(II) coordination number of 4.5 in the resting enzyme appears to be maintained throughout the reaction with nitrocefin. This is the first direct structural information available on early stage dizinc metallo-β-lactamase catalysis
System for monitoring and controlling unit operations that include distillation
Fluid sensor methods and systems adapted for monitoring and/or controlling distillation operations in fluidic systems, such as bath distillation operations or continuous distillation operations, are disclosed. Preferred embodiments are directed to process monitoring and/or process control for unit operations involving endpoint determination of a distillation, for example, as applied to a liquid-component-switching operation (e.g., a solvent switehing operation), a liquid-liquid separation operation, a solute concentration operation, a dispersed- phase concentration operation, among others
Compression Bases in Unital Groups
We study unital groups with a distinguished family of compressions called a
compression base. A motivating example is the partially ordered additive group
of a von Neumann algebra with all Naimark compressions as the compression base.Comment: 8 page
Posttraumatic Attenuation of the Lisfranc Ligament in a 14-Year-Old Athlete: A Case Report
Lisfranc injuries in children are rare and range from mild midfoot sprains to severe traumatic fracture-dislocations. Management of sprains is nonoperative, whereas treatment of fracture-dislocations often requires internal fixation. We present a unique case of a midfoot sprain in a 14-year-old adolescent boy, with gradual increased instability at the joint owing to attenuation of the Lisfranc ligament. Closed reduction and percutaneous pinning resulted in successful treatment at 3 weeks postoperatively. Midfoot sprains may lead to further ligamentous attenuation and widening as seen on radiographs and thus should be monitored for signs of persistent pain and instability. Because midfoot instability contributes considerably to posttraumatic arthritis, we recommend reduction when nonoperative interventions are unsuccessful
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