791 research outputs found
On the discrete spectrum of quantum layers
Consider a quantum particle trapped between a curved layer of constant width
built over a complete, non-compact, smooth surface embedded in
. We assume that the surface is asymptotically flat in the sense
that the second fundamental form vanishes at infinity, and that the surface is
not totally geodesic. This geometric setting is known as a quantum layer. We
consider the quantum particle to be governed by the Dirichlet Laplacian as
Hamiltonian. Our work concerns the existence of bound states with energy
beneath the essential spectrum, which implies the existence of discrete
spectrum. We first prove that if the Gauss curvature is integrable, and the
surface is weakly -parabolic, then the discrete spectrum is non-empty.
This result implies that if the total Gauss curvature is non-positive, then the
discrete spectrum is non-empty. We next prove that if the Gauss curvature is
non-negative, then the discrete spectrum is non-empty. Finally, we prove that
if the surface is parabolic, then the discrete spectrum is non-empty if the
layer is sufficiently thin.Comment: Clarifications and corrections to previous version, conjecture from
previous version is proven here (Theorem 1.5), additional references include
Vesicle shape, molecular tilt, and the suppression of necks
Can the presence of molecular-tilt order significantly affect the shapes of
lipid bilayer membranes, particularly membrane shapes with narrow necks?
Motivated by the propensity for tilt order and the common occurrence of narrow
necks in the intermediate stages of biological processes such as endocytosis
and vesicle trafficking, we examine how tilt order inhibits the formation of
necks in the equilibrium shapes of vesicles. For vesicles with a spherical
topology, point defects in the molecular order with a total strength of
are required. We study axisymmetric shapes and suppose that there is a
unit-strength defect at each pole of the vesicle. The model is further
simplified by the assumption of tilt isotropy: invariance of the energy with
respect to rotations of the molecules about the local membrane normal. This
isotropy condition leads to a minimal coupling of tilt order and curvature,
giving a high energetic cost to regions with Gaussian curvature and tilt order.
Minimizing the elastic free energy with constraints of fixed area and fixed
enclosed volume determines the allowed shapes. Using numerical calculations, we
find several branches of solutions and identify them with the branches
previously known for fluid membranes. We find that tilt order changes the
relative energy of the branches, suppressing thin necks by making them costly,
leading to elongated prolate vesicles as a generic family of tilt-ordered
membrane shapes.Comment: 10 pages, 7 figures, submitted to Phy. Rew.
Dynamics of filaments and membranes in a viscous fluid
Motivated by the motion of biopolymers and membranes in solution, this
article presents a formulation of the equations of motion for curves and
surfaces in a viscous fluid. We focus on geometrical aspects and simple
variational methods for calculating internal stresses and forces, and we derive
the full nonlinear equations of motion. In the case of membranes, we pay
particular attention to the formulation of the equations of hydrodynamics on a
curved, deforming surface. The formalism is illustrated by two simple case
studies: (1) the twirling instability of straight elastic rod rotating in a
viscous fluid, and (2) the pearling and buckling instabilities of a tubular
liposome or polymersome.Comment: 26 pages, 12 figures, to be published in Reviews of Modern Physic
Grass-finished Beef Pilot Project: Cattle Performance
Consumer interest in the potential benefits of grass-finished beef is high, but adoption of this approach to cattle feeding has been limited in Iowa. Although some producers successfully meet this niche market demand, consistently producing a high-value carcass from forage-fed cattle is challenging. Intramuscular fat or marbling is a major factor in quality grading of beef. Marbling is heavily influenced by cattle genetics and energy concentration of the diet. Finishing cattle on grain is a proven approach to consistently produce a high-value carcass for the commodity beef market. Researchers at Iowa State University have pioneered the use of ultrasound measurements to select Angus cattle with high-marbling potential. Forage quality can be manipulated through pasture management, ultimately influencing cattle growth and performance. It is hypothesized that grass-finished cattle will consistently produce high value carcasses if excellent pasture management is combined with combining high-marbling genetics
Towards a sensitive search for variation of the fine structure constant using radio-frequency E1 transitions in atomic dysprosium
It has been proposed that the radio-frequency electric-dipole (E1) transition
between two nearly degenerate opposite-parity states in atomic dysprosium
should be highly sensitive to possible temporal variation of the fine structure
constant () [V. A. Dzuba, V. V. Flambaum, and J. K. Webb, Phys. Rev. A
{\bf 59}, 230 (1999)]. We analyze here an experimental realization of the
proposed search in progress in our laboratory, which involves monitoring the E1
transition frequency over a period of time using direct frequency counting
techniques. We estimate that a statistical sensitivity of |\adota| \sim
10^{-18}/yr may be achieved and discuss possible systematic effects that may
limit such a measurement.Comment: 8 pages, 7 figure
Pain Management in the Neonatal Piglet During Routine Management Procedures. Part 1: A Systematic Review of Randomized and Non-Randomized Intervention Studies
Routine procedures carried out on piglets (i.e. castration, tail docking, teeth clipping, and ear notching) are considered painful. Unfortunately the efficacy of current pain mitigation modalities is poorly understood. The aim of this systematic review was to synthesize the existing primary scientific literature regarding the effectiveness of pain management interventions used for routine procedures on piglets. The review question was, \u27In piglets under twenty-eight days old, undergoing castration, tail docking, teeth clipping, and/or methods of identification that involve cutting of the ear tissue, what is the effect of pain mitigation compared with no pain mitigation on behavioral and non-behavioral outcomes that indicate procedural pain and post-procedural pain?\u27 A review protocol was designed a priori. Data sources used were Agricola (EBSCO), CAB Abstracts (Thomson Reuters), PubMed, Web of Science (Thomson Reuters), BIOSIS Previews (Thomson Reuters), and ProQuest Dissertations & Theses Full Text. No restrictions on year of publication or language were placed on the search. Eligible studies assessed an intervention designed to mitigate the pain of the procedures of interest and included a comparison group that did not receive an intervention. Eligible non-English studies were translated using a translation service. Two reviewers independently screened titles and abstracts for relevance using pre-defined questions. Data were extracted from relevant articles onto pre-defined forms. From the 2203 retrieved citations forty publications, containing 52 studies met the eligibility criteria. In 40 studies, piglets underwent castration only. In seven studies, piglets underwent tail docking only. In one study, piglets underwent teeth clipping only, and in one study piglets underwent ear notching only. Three studies used multiple procedures. Thirty-two trial arms assessed general anesthesia protocols, 30 trial arms assessed local anesthetic protocols, and 28 trial arms assessed non-steroidal anti-inflammatory drugs (NSAIDs) protocols. Forty-one trial arms were controls where piglets received either placebo or no treatment. Forty-five outcomes were extracted from the studies, however only the results from studies that assessed cortisol (six studies), β-endorphins (one study), vocalisations (nine studies), and pain-related behaviors (nine studies) are reported. Other outcomes were reported in only one or two studies. Confident decision making will likely be difficult based on this body of work because lack of comprehensive reporting precludes calculation of the magnitude of pain mitigation for most outcomes
Pain management in the neonatal piglet during routine management procedures. Part 2:Grading the quality of evidence and the strength of recommendations
Piglets reared in swine production in the USA undergo painful procedures that include castration, tail docking, teeth clipping, and identification with ear notching or tagging. These procedures are usually performed without pain mitigation. The objective of this project was to develop recommendations for pain mitigation in 1- to 28-day-old piglets undergoing these procedures. The National Pork Board funded project to develop recommendations for pain mitigation in piglets. Recommendation development followed a defined multi-step process that included an evidence summary and estimates of the efficacies of interventions. The results of a systematic review of the interventions were reported in a companion paper. This manuscript describes the recommendation development process and the final recommendations. Recommendations were developed for three interventions (CO2/O2 general anesthesia, non-steroidal anti-inflammatory drugs (NSAIDs), and lidocaine) for use during castration. The ability to make strong recommendations was limited by low-quality evidence and strong certainty about variation in stakeholder values and preferences. The panel strongly recommended against the use of a CO2/O2 general anesthesia mixture, weakly recommended for the use of NSAIDs and weakly recommended against the use of lidocaine for pain mitigation during castration of 1- to 28-day-old piglets
The compensation of Gaussian curvature in developable cones is local
In this paper we use the angular deficit scheme [V. Borrelli, F. Cazals, and
J.-M. Morvan, {\sl Computer Aided Geometric Design} {\bf 20}, 319 (2003)] to
determine the distribution of Gaussian curvature in developable cones (d-cones)
[E. Cerda, S. Chaieb, F. Melo, and L. Mahadevan, {\sl Nature} {\bf 401}, 46
(1999)] numerically. These d-cones are formed by pushing a thin elastic sheet
into a circular container. Negative Gaussian curvatures are identified at the
rim where the sheet touches the container. Around the rim there are two narrow
bands with positive Gaussian curvatures. The integral of the (negative)
Gaussian curvature near the rim is almost completely compensated by that of the
two adjacent bands. This suggests that the Gauss-Bonnet theorem which
constrains the integral of Gaussian curvature globally does not explain the
spontaneous curvature cancellation phenomenon [T. Liang and T. A. Witten, {\sl
Phys. Rev. E} {\bf 73}, 046604 (2006)]. The locality of the compensation seems
to increase for decreasing d-cone thickness. The angular deficit scheme also
provides a new way to confirm the curvature cancellation phenomenon.Comment: 12 pages; 5 figure
Interoception in functional motor symptoms and functional seizures: preliminary evidence of intact accuracy alongside reduced insight and altered sensibility
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