3,390 research outputs found
A conventional point of view on active magnetic bearings
Active magnetic bearings used in rotating machinery should be designed as locally controlled, independent devices similar to other types of bearings. The functions of control electronics and power amplifiers can be simply and explicitly related to general bearing properties such as load capacity, stiffness, and damping. The dynamics of a rotor and its supporting active magnetic bearings are analyzed in a modified conventional method with an extended state vector containing the bearing state variables
Unsteady thermocapillary migration of bubbles
Upon the introduction of a gas bubble into a liquid possessing a uniform thermal gradient, an unsteady thermo-capillary flow begins. Ultimately, the bubble attains a constant velocity. This theoretical analysis focuses upon the transient period for a bubble in a microgravity environment and is restricted to situations wherein the flow is sufficiently slow such that inertial terms in the Navier-Stokes equation and convective terms in the energy equation may be safely neglected (i.e., both Reynolds and Marangoni numbers are small). The resulting linear equations were solved analytically in the Laplace domain with the Prandtl number of the liquid as a parameter; inversion was accomplished numerically using a standard IMSL routine. In the asymptotic long-time limit, the theory agrees with the steady-state theory of Young, Goldstein, and Block. The theory predicts that more than 90 percent of the terminal steady velocity is achieved when the smallest dimensionless time, i.e., the one based upon the largest time scale-viscous or thermal-equals unity
On induced birefringence in viscoelastic materials
Describing induced birefringence in viscoelastic materials based on constitutive assumptions for stress and dielectric propertie
Evolution of the potential-energy surface of amorphous silicon
The link between the energy surface of bulk systems and their dynamical
properties is generally difficult to establish. Using the activation-relaxation
technique (ART nouveau), we follow the change in the barrier distribution of a
model of amorphous silicon as a function of the degree of relaxation. We find
that while the barrier-height distribution, calculated from the initial
minimum, is a unique function that depends only on the level of distribution,
the reverse-barrier height distribution, calculated from the final state, is
independent of the relaxation, following a different function. Moreover, the
resulting gained or released energy distribution is a simple convolution of
these two distributions indicating that the activation and relaxation parts of
a the elementary relaxation mechanism are completely independent. This
characterized energy landscape can be used to explain nano-calorimetry
measurements.Comment: 5 pages, 4 figure
Sequence Heterogeneity Accelerates Protein Search for Targets on DNA
The process of protein search for specific binding sites on DNA is
fundamentally important since it marks the beginning of all major biological
processes. We present a theoretical investigation that probes the role of DNA
sequence symmetry, heterogeneity and chemical composition in the protein search
dynamics. Using a discrete-state stochastic approach with a first-passage
events analysis, which takes into account the most relevant physical-chemical
processes, a full analytical description of the search dynamics is obtained. It
is found that, contrary to existing views, the protein search is generally
faster on DNA with more heterogeneous sequences. In addition, the search
dynamics might be affected by the chemical composition near the target site.
The physical origins of these phenomena are discussed. Our results suggest that
biological processes might be effectively regulated by modifying chemical
composition, symmetry and heterogeneity of a genome.Comment: 10 pages, 5 figure
TB128: Beauveria bassiana for Control of Colorado Potato Beetle (Coleoptera: Chrysomelidae) in Maine
Beauveria bassiana (Balsamo) Vuill. (Bb), a fungal pathogen of the Colorado potato beetle has been used to control CPB in Europe. Preliminary studies in the United States gave promising results for CPB control by using the fungus. Based on these studies, a three-year pilot program was initiated to evaluate the potential for using Bb o control the Colorado potato beetle in the U.S. We report herein on the results obtained in southern Maine from using this mycoinsecticide to control the beetle.https://digitalcommons.library.umaine.edu/aes_techbulletin/1064/thumbnail.jp
Highly Designable Protein Structures and Inter Monomer Interactions
By exact computer enumeration and combinatorial methods, we have calculated
the designability of proteins in a simple lattice H-P model for the protein
folding problem.
We show that if the strength of the non-additive part of the interaction
potential becomes larger than a critical value, the degree of designability of
structures will depend on the parameters of potential. We also show that the
existence of a unique ground state is highly sensitive to mutation in certain
sites.Comment: 14 pages, Latex file, 3 latex and 6 eps figures are include
- …