2,503 research outputs found
Simulations of the angular dependence of the dipole-dipole interaction among Rydberg atoms
The dipole-dipole interaction between two Rydberg atoms depends on the
relative orientation of the atoms and on the change in the magnetic quantum
number. We simulate the effect of this anisotropy on the energy transport in an
amorphous many atom system subject to a homogeneous applied electric field. We
consider two experimentally feasible geometries and find that the effects
should be measurable in current generation imaging experiments. In both
geometries atoms of character are localized to a small region of space
which is immersed in a larger region that is filled with atoms of
character. Energy transfer due to the dipole-dipole interaction can lead to a
spread of character into the region initially occupied by atoms. Over
long timescales the energy transport is confined to the volume near the border
of the region which is suggestive of Anderson localization. We calculate a
correlation length of 6.3~m for one particular geometry.Comment: 6 pages, 5 figures, revised draf
Supersymmetric Electroweak Baryogenesis Via Resonant Sfermion Sources
We calculate the baryon asymmetry produced at the electroweak phase
transition by quasi-degenerate third generation sfermions in the minimal
supersymmetric extension of the Standard Model. We evaluate constraints from
Higgs searches, from collider searches for supersymmetric particles, and from
null searches for the permanent electric dipole moment (EDM) of the electron,
of the neutron and of atoms. We find that resonant sfermion sources can in
principle provide a large enough baryon asymmetry in various corners of the
sfermion parameter space, and we focus, in particular, on the case of large
, where third-generation down-type (s)fermions become relevant. We
show that in the case of stop and sbottom sources, the viable parameter space
is ruled out by constraints from the non-observation of the Mercury EDM. We
introduce a new class of CP violating sources, quasi-degenerate staus, that
escapes current EDM constraints while providing large enough net chiral
currents to achieve successful "slepton-mediated" electroweak baryogenesis.Comment: 35 pages, 9 figures; v2: several revisions, but conclusions
unchanged. Matches version published in PR
Geometry and Destiny
The recognition that the cosmological constant may be non-zero forces us to
re-evaluate standard notions about the connection between geometry and the fate
of our Universe. An open Universe can recollapse, and a closed Universe can
expand forever. As a corollary, we point out that there is no set of
cosmological observations we can perform that will unambiguously allow us to
determine what the ultimate destiny of the Universe will be.Comment: 7 pages, Gravity Research Foundation Essa
Phase Transitions and Gauge Artifacts in an Abelian Higgs Plus Singlet Model
While the finite-temperature effective potential in a gauge theory is a
gauge-dependent quantity, in several instances a first-order phase transition
can be triggered by gauge-independent terms. A particularly interesting case
occurs when the potential barrier separating the broken and symmetric vacua of
a spontaneously broken symmetry is produced by tree-level terms in the
potential. Here, we study this scenario in a simple Abelian Higgs model, for
which the gauge-invariant potential is known, augmented with a singlet real
scalar. We analyze the possible symmetry breaking patterns in the model, and
illustrate in which cases gauge artifacts are expected to manifest themselves
most severely. We then show that gauge artifacts can be pronounced even in the
presence of a relatively large, tree-level singlet-Higgs cubic interaction.
When the transition is strongly first order, these artifacts, while present,
are more subtle than in the generic situation.Comment: 19 pages, 4 figures. Added comparisons with a gauge-independent
formalism (which necessitated removing the counterterms from the original
model), and fixed a computational error in the effective potential. Figures
2, 3, and 4 are changed, along with much of section 3. The qualitative
results remain the sam
Soil Moisture Survey
Each spring and fall a soil moisture survey is conducted to determine the amount of plant-available moisture in the top five feet of many of the major soils in Iowa. Several of the sites are located in the Wallace Foundation for Rural Research and Development (WFRRD) area. Many producers make or alter their crop management plans according to expected soil moisture levels
Effect of silver content on the structure and antibacterial activity of silver-doped phosphate-based glasses
Staphylococcus aureus can cause a range of diseases, such as osteomyelitis, as well as colonize implanted medical devices. In most instances the organism forms biofilms that not only are resistant to the body's defense mechanisms but also display decreased susceptibilities to antibiotics. In the present study, we have examined the effect of increasing silver contents in phosphate-based glasses to prevent the formation of S. aureus biofilms. Silver was found to be an effective bactericidal agent against S. aureus biofilms, and the rate of silver ion release (0.42 to 1.22 µg·mm–2·h–1) from phosphate-based glass was found to account for the variation in its bactericidal effect. Analysis of biofilms by confocal microscopy indicated that they consisted of an upper layer of viable bacteria together with a layer (20 µm) of nonviable cells on the glass surface. Our results showed that regardless of the silver contents in these glasses (10, 15, or 20 mol%) the silver exists in its +1 oxidation state, which is known to be a highly effective bactericidal agent compared to that of silver in other oxidation states (+2 or +3). Analysis of the glasses by 31P nuclear magnetic resonance imaging and high-energy X-ray diffraction showed that it is the structural rearrangement of the phosphate network that is responsible for the variation in silver ion release and the associated bactericidal effectiveness. Thus, an understanding of the glass structure is important in interpreting the in vitro data and also has important clinical implications for the potential use of the phosphate-based glasses in orthopedic applications to deliver silver ions to combat S. aureus biofilm infections
Nano-enabled synthetic biology
Biological systems display a functional diversity, density and efficiency that make them a paradigm for synthetic systems. In natural systems, the cell is the elemental unit and efforts to emulate cells, their components, and organization have relied primarily on the use of bioorganic materials. Impressive advances have been made towards assembling simple genetic systems within cellular scale containers. These biological system assembly efforts are particularly instructive, as we gain command over the directed synthesis and assembly of synthetic nanoscale structures. Advances in nanoscale fabrication, assembly, and characterization are providing the tools and materials for characterizing and emulating the smallest scale features of biology. Further, they are revealing unique physical properties that emerge at the nanoscale. Realizing these properties in useful ways will require attention to the assembly of these nanoscale components. Attention to systems biology principles can lead to the practical development of nanoscale technologies with possible realization of synthetic systems with cell-like complexity. In turn, useful tools for interpreting biological complexity and for interfacing to biological processes will result
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