203 research outputs found
Retarded long-range potentials for the alkali-metal atoms and a perfectly conducting wall
The retarded long-range potentials for hydrogen and alkali-metal atoms in
their ground states and a perfectly conducting wall are calculated. The
potentials are given over a wide range of atom-wall distances and the validity
of the approximations used is established.Comment: RevTeX, epsf, 11 pages, 2 fig
Matter-field theory of the Casimir force
A matter-field theory of the Casimir force is formulated in which the
electromagnetic field and collective modes of dielectric media are treated on
an equal footing. In our theory, the Casimir force is attributed to zero-point
energies of the combined matter-field modes. We analyze why some of the
existing theories favor the interpretation of the Casimir force as originating
from zero-point energies of the electromagnetic field and others from those of
the matter.Comment: 12pages, 1 Postscript figur
Using atomic interference to probe atom-surface interaction
We show that atomic interference in the reflection from two suitably
polarized evanescent waves is sensitive to retardation effects in the
atom-surface interaction for specific experimental parameters. We study the
limit of short and long atomic de Broglie wavelength. The former case is
analyzed in the semiclassical approximation (Landau-Zener model). The latter
represents a quantum regime and is analyzed by solving numerically the
associated coupled Schroedinger equations. We consider a specific experimental
scheme and show the results for rubidium (short wavelength) and the much
lighter meta-stable helium atom (long wavelength). The merits of each case are
then discussed.Comment: 11 pages, including 6 figures, submitted to Phys. Rev. A, RevTeX
sourc
Higgs- and Goldstone bosons-mediated long range forces
In certain mild extensions of the Standard Model, spin-independent long range
forces can arise by exchange of two very light pseudoscalar spin--0 bosons. In
particular, we have in mind models in which these bosons do not have direct
tree level couplings to ordinary fermions. Using the dispersion theoretical
method, we find a behaviour of the potential for the exchange of very
light pseudoscalars and a dependence if the pseudoscalars are true
massless Goldstone bosons.Comment: 13 pages (REVTeX), 2 figure
Strong Interactions of Single Atoms and Photons near a Dielectric Boundary
Modern research in optical physics has achieved quantum control of strong
interactions between a single atom and one photon within the setting of cavity
quantum electrodynamics (cQED). However, to move beyond current
proof-of-principle experiments involving one or two conventional optical
cavities to more complex scalable systems that employ N >> 1 microscopic
resonators requires the localization of individual atoms on distance scales <
100 nm from a resonator's surface. In this regime an atom can be strongly
coupled to a single intracavity photon while at the same time experiencing
significant radiative interactions with the dielectric boundaries of the
resonator. Here, we report an initial step into this new regime of cQED by way
of real-time detection and high-bandwidth feedback to select and monitor single
Cesium atoms localized ~100 nm from the surface of a micro-toroidal optical
resonator. We employ strong radiative interactions of atom and cavity field to
probe atomic motion through the evanescent field of the resonator. Direct
temporal and spectral measurements reveal both the significant role of
Casimir-Polder attraction and the manifestly quantum nature of the atom-cavity
dynamics. Our work sets the stage for trapping atoms near micro- and
nano-scopic optical resonators for applications in quantum information science,
including the creation of scalable quantum networks composed of many
atom-cavity systems that coherently interact via coherent exchanges of single
photons.Comment: 8 pages, 5 figures, Supplemental Information included as ancillary
fil
Impairment experiences, identity and attitudes towards genetic screening : the views of people with Spinal Muscular Atrophy
Developments in genetics are rapidly changing the capacity and scope of screening practices. However, people with genetic conditions have been under-represented in the literature exploring their implications. This mixed methods study explores the attitudes of people with Spinal Muscular Atrophy (SMA) towards three different population-level genetic screening programmes for SMA: pre-conception, prenatal and newborn. Drawing on qualitative interviews (n= 15) and a survey (n=82), this study demonstrates that more severely affected individuals with early-onset symptoms (Type II SMA), are less likely to support screening and more likely to view SMA positively than those with milder, later onset and/or fluctuating symptoms (Types III/ IV SMA). Indeed, this clinically milder group were more likely to support all forms of screening and view SMA negatively. This paper highlights that screening is a complex issue for people with genetic conditions, and the nature of impairment experiences plays a critical role in shaping attitudes
Casimir interaction between a microscopic dipole oscillator and a macroscopic solenoid
We discuss the interaction between a microscopic electric dipole oscillator and a long solenoid which are separated by a small distance. The solenoid belongs to a simple RLC circuit and the zero point and thermal current fluctuations within the solenoid coils are taken into account. We describe how they affect the equilibrium state and the excited states of the oscillator, thus providing a description of the Casimir interaction of the system. We calculate the modification in the lifetime of the oscillator excited states as a function of the parameters of the circuit, the dipole orientation, and the distance between the dipole and the solenoid. The Casimir force between the solenoid and the electric dipole is calculated, and it is shown that this Casimir interaction always exists, that is, it occurs even when the macroscopic current in the solenoid is zero. We suggest experiments which can exhibit these effects related to the electromagnetic interactions between atoms or molecules and simple circuits
The Effect of Diel Temperature and Light Cycles on the Growth of Nannochloropsis oculata in a Photobioreactor Matrix
A matrix of photobioreactors integrated with metabolic sensors was used to examine the combined impact of light and temperature variations on the growth and physiology of the biofuel candidate microalgal species Nannochloropsis oculata. The experiments were performed with algal cultures maintained at a constant 20u C versus a 15°C to 25°C diel temperature cycle, where light intensity also followed a diel cycle with a maximum irradiance of 1920 μmol photons m-2 s-1. No differences in algal growth (Chlorophyll a) were found between the two environmental regimes; however, the metabolic processes responded differently throughout the day to the change in environmental conditions. The variable temperature treatment resulted in greater damage to photosystem II due to the combined effect of strong light and high temperature. Cellular functions responded differently to conditions before midday as opposed to the afternoon, leading to strong hysteresis in dissolved oxygen concentration, quantum yield of photosystem II and net photosynthesis. Overnight metabolism performed differently, probably as a result of the temperature impact on respiration. Our photobioreactor matrix has produced novel insights into the physiological response of Nannochloropsis oculata to simulated environmental conditions. This information can be used to predict the effectiveness of deploying Nannochloropsis oculata in similar field conditions for commercial biofuel production. © 2014 Tamburic et al
Adjusted Light and Dark Cycles Can Optimize Photosynthetic Efficiency in Algae Growing in Photobioreactors
Biofuels from algae are highly interesting as renewable energy sources to replace, at least partially, fossil fuels, but great research efforts are still needed to optimize growth parameters to develop competitive large-scale cultivation systems. One factor with a seminal influence on productivity is light availability. Light energy fully supports algal growth, but it leads to oxidative stress if illumination is in excess. In this work, the influence of light intensity on the growth and lipid productivity of Nannochloropsis salina was investigated in a flat-bed photobioreactor designed to minimize cells self-shading. The influence of various light intensities was studied with both continuous illumination and alternation of light and dark cycles at various frequencies, which mimic illumination variations in a photobioreactor due to mixing. Results show that Nannochloropsis can efficiently exploit even very intense light, provided that dark cycles occur to allow for re-oxidation of the electron transporters of the photosynthetic apparatus. If alternation of light and dark is not optimal, algae undergo radiation damage and photosynthetic productivity is greatly reduced. Our results demonstrate that, in a photobioreactor for the cultivation of algae, optimizing mixing is essential in order to ensure that the algae exploit light energy efficiently
Specific Recognition of p53 Tetramers by Peptides Derived from p53 Interacting Proteins
Oligomerization plays a major role in regulating the activity of many proteins, and in modulating their interactions. p53 is a homotetrameric transcription factor that has a pivotal role in tumor suppression. Its tetramerization domain is contained within its C-terminal domain, which is a site for numerous protein-protein interactions. Those can either depend on or regulate p53 oligomerization. Here we screened an array of peptides derived from proteins known to bind the tetrameric p53 C-terminal domain (p53CTD) and identified ten binding peptides. We quantitatively characterized their binding to p53CTD using fluorescence anisotropy. The peptides bound tetrameric p53CTD with micromolar affinities. Despite the high charge of the binding peptides, electrostatics contributed only mildly to the interactions. NMR studies indicated that the peptides bound p53CTD at defined sites. The most significant chemical shift deviations were observed for the peptides WS100B(81–92), which bound directly to the p53 tetramerization domain, and PKCα(281–295), which stabilized p53CTD in circular dichroism thermal denaturation studies. Using analytical ultracentrifugation, we found that several of the peptides bound preferentially to p53 tetramers. Our results indicate that the protein-protein interactions of p53 are dependent on the oligomerization state of p53. We conclude that peptides may be used to regulate the oligomerization of p53
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