319 research outputs found
Stimulated Raman Adiabatic Passage (STIRAP) Among Degenerate-Level Manifolds
We examine the conditions needed to accomplish stimulated Raman adiabatic
passage (STIRAP) when the three levels (g, e and f) are degenerate, with
arbitrary couplings contributing to the pump-pulse interaction (g - e) and to
the Stokes-pulse interaction (e-f). We show that in general a sufficient
condition for complete population removal from the g set of degenerate states
for arbitrary, pure or mixed, initial state is that the degeneracies should not
decrease along the sequence g, e and f. We show that when this condition holds
it is possible to achieve the degenerate counterpart of conventional STIRAP,
whereby adiabatic passage produces complete population transfer. Indeed, the
system is equivalent to a set of independent three-state systems, in each of
which a STIRAP procedure can be implemented. We describe a scheme of unitary
transformations that produces this result. We also examine the cases when this
degeneracy constraint does not hold, and show what can be accomplished in those
cases. For example, for angular momentum states when the degeneracy of the g
and f levels is less than that of the e level we show how a special choice for
the pulse polarizations and phases can produce complete removal of population
from the g set. Our scheme can be a powerful tool for coherent control in
degenerate systems, because of its robustness when selective addressing of the
states is not required or impossible. We illustrate the analysis with several
analytically solvable examples, in which the degeneracies originate from
angular momentum orientation, as expressed by magnetic sublevels.Comment: 21 pages, 17 figure
Competitive stochastic noises in coherently driven two-level atoms and quantum interference
A system of coherently-driven two-level atoms is analyzed in presence of two
independent stochastic perturbations: one due to collisions and a second one
due to phase fluctuations of the driving field. The behaviour of the quantum
interference induced by the collisional noise is considered in detail. The
quantum-trajectory method is utilized to reveal the phase correlations between
the dressed states involved in the interfering transition channels. It is shown
that the quantum interference induced by the collisional noise is remarkably
robust against phase noise. This effect is due to the fact that the phase
noise, similarly to collisions, stabilizes the phase-difference between the
dressed states.Comment: accepted for publication in J. Opt.
Adiabatic creation of coherent superposition states via multiple intermediate states
We consider an adiabatic population transfer process that resembles the well
established stimulated Raman adiabatic passage (STIRAP). In our system, the
states have nonzero angular momentums , therefore, the coupling laser fields
induce transitions among the magnetic sublevels of the states. In particular,
we discuss the possibility of creating coherent superposition states in a
system with coupling pattern and . Initially, the system is in the J=0 state. We show that by two delayed,
overlapping laser pulses it is possible to create any final superposition state
of the magnetic sublevels , , . Moreover, we find that
the relative phases of the applied pulses influence not only the phases of the
final superposition state but the probability amplitudes as well. We show that
if we fix the shape and the time-delay between the pulses, the final state
space can be entirely covered by varying the polarizations and relative phases
of the two pulses. Performing numerical simulations we find that our transfer
process is nearly adiabatic for the whole parameter set.Comment: 7 pages, 10 figure
Ultrasound increases plasmid-mediated gene transfer to dystrophic muscles without collateral damage
Studies have shown that ultrasound, used either alone or in combination with microbubble contrast agents, can increase cell membrane permeability to plasmid DNA. Because ultrasound is a non-painful and well-established tool in clinical medicine, its potential to enhance DNA uptake into the muscles of patients with muscular dystrophy is conceptually attractive. Therefore, we evaluated the ability of ultrasound pulses (1 MHz; 1.5 W/cm2) to increase exogenous (LacZ) gene expression in normal wild-type and dystrophic Dmd(mdx/mdx) mice after plasmid DNA injection into muscle. We also ascertained whether co-injection of lipid-encapsulated perfluoropropane microbubbles (Definity) or pretreatment with hyaluronidase could further increase the level of gene transfer to ultrasound-treated muscles. The use of ultrasound did not increase transfection efficiency in normal mice. In contrast, dystrophic mice demonstrated an increase in the number of transfected fibers (threefold) as well as the amount of LacZ protein (22-fold) after ultrasound exposure, provided that Definity was also co-injected with the DNA. Pretreatment of muscles with hyaluronidase before ultrasound exposure was not effective in augmenting the level of gene transfer. Under the optimal conditions for dystrophic muscle transfection (ultrasound + Definity), there was no associated increase in muscle damage. Hence ultrasound may provide a safe and effective method for enhancing gene transfer to dystrophic muscles, thereby increasing the prospects for therapeutic application of naked DNA in muscular dystrophy patients.Peer reviewed: YesNRC publication: N
The Infrared Array Camera (IRAC) for the Spitzer Space Telescope
The Infrared Array Camera (IRAC) is one of three focal plane instruments in
the Spitzer Space Telescope. IRAC is a four-channel camera that obtains
simultaneous broad-band images at 3.6, 4.5, 5.8, and 8.0 microns. Two nearly
adjacent 5.2x5.2 arcmin fields of view in the focal plane are viewed by the
four channels in pairs (3.6 and 5.8 microns; 4.5 and 8 microns). All four
detector arrays in the camera are 256x256 pixels in size, with the two shorter
wavelength channels using InSb and the two longer wavelength channels using
Si:As IBC detectors. IRAC is a powerful survey instrument because of its high
sensitivity, large field of view, and four-color imaging. This paper summarizes
the in-flight scientific, technical, and operational performance of IRAC.Comment: 7 pages, 3 figures. Accepted for publication in the ApJS. A higher
resolution version is at http://cfa-www.harvard.edu/irac/publication
Age- and Gender-Related Changes in Contractile Properties of Non-Atrophied EDL Muscle
Background: In humans, ageing causes skeletal muscles to become atrophied, weak, and easily fatigued. In rodent studies, ageing has been associated with significant muscle atrophy and changes in the contractile properties of the muscles. However, it is not entirely clear whether these changes in contractile properties can occur before there is significant atrophy, and whether males and females are affected differently. Methods and Results: We investigated various contractile properties of whole isolated fast-twitch EDL muscles from adult (2–6 months-old) and aged (12–22 months-old) male and female mice. Atrophy was not present in the aged mice. Compared with adult mice, EDL muscles of aged mice had significantly lower specific force, longer tetanus relaxation times, and lower fatiguability. In the properties of absolute force and muscle relaxation times, females were affected by ageing to a greater extent than males. Additionally, EDL muscles from a separate group of male mice were subjected to eccentric contractions of 15 % strain, and larger force deficits were found in aged than in adult mice. Conclusion: Our findings provide further insight into the muscle atrophy, weakness and fatiguability experienced by the elderly. We have shown that even in the absence of muscle atrophy, there are definite alterations in the physiological properties of whole fast-twitch muscle from ageing mice, and for some of these properties the alterations are mor
AAV-mediated intramuscular delivery of myotubularin corrects the myotubular myopathy phenotype in targeted murine muscle and suggests a function in plasma membrane homeostasis
Myotubular myopathy (XLMTM, OMIM 310400) is a severe congenital muscular disease due to mutations in the myotubularin gene (MTM1) and characterized by the presence of small myofibers with frequent occurrence of central nuclei. Myotubularin is a ubiquitously expressed phosphoinositide phosphatase with a muscle-specific role in man and mouse that is poorly understood. No specific treatment exists to date for patients with myotubular myopathy. We have constructed an adeno-associated virus (AAV) vector expressing myotubularin in order to test its therapeutic potential in a XLMTM mouse model. We show that a single intramuscular injection of this vector in symptomatic Mtm1-deficient mice ameliorates the pathological phenotype in the targeted muscle. Myotubularin replacement in mice largely corrects nuclei and mitochondria positioning in myofibers and leads to a strong increase in muscle volume and recovery of the contractile force. In addition, we used this AAV vector to overexpress myotubularin in wild-type skeletal muscle and get insight into its localization and function. We show that a substantial proportion of myotubularin associates with the sarcolemma and I band, including triads. Myotubularin overexpression in muscle induces the accumulation of packed membrane saccules and presence of vacuoles that contain markers of sarcolemma and T-tubules, suggesting that myotubularin is involved in plasma membrane homeostasis of myofibers. This study provides a proof-of-principle that local delivery of an AAV vector expressing myotubularin can improve the motor capacities of XLMTM muscle and represents a novel approach to study myotubularin function in skeletal muscle
Science and society in education
This booklet is for teachers who want to expand their
teaching approaches to include socio-scientific issues
which enrich and give meaning to core scientific principles.
It is meant to enhance young people’s curiosity about the
social and scientific world and raise important questions
about issues which affect their lives. We call this approach
Socio-Scientific Inquiry-Based Learning, or ‘SSIBL’ for
short. Chapters 1 and 2 present an introduction to the
theoretical background of SSIBL. In chapter 3, SSIBL will
be approached from a classroom perspective, providing a
simplified version of the framework and showing teaching
examples
Muscle Fiber Viability, a Novel Method for the Fast Detection of Ischemic Muscle Injury in Rats
Acute lower extremity ischemia is a limb- and life-threatening clinical problem. Rapid detection of the degree of injury is crucial, however at present there are no exact diagnostic tests available to achieve this purpose. Our goal was to examine a novel technique - which has the potential to accurately assess the degree of ischemic muscle injury within a short period of time - in a clinically relevant rodent model. Male Wistar rats were exposed to 4, 6, 8 and 9 hours of bilateral lower limb ischemia induced by the occlusion of the infrarenal aorta. Additional animals underwent 8 and 9 hours of ischemia followed by 2 hours of reperfusion to examine the effects of revascularization. Muscle samples were collected from the left anterior tibial muscle for viability assessment. The degree of muscle damage (muscle fiber viability) was assessed by morphometric evaluation of NADH-tetrazolium reductase reaction on frozen sections. Right hind limbs were perfusion-fixed with paraformaldehyde and glutaraldehyde for light and electron microscopic examinations. Muscle fiber viability decreased progressively over the time of ischemia, with significant differences found between the consecutive times. High correlation was detected between the length of ischemia and the values of muscle fiber viability. After reperfusion, viability showed significant reduction in the 8-hour-ischemia and 2-hour-reperfusion group compared to the 8-hour-ischemia-only group, and decreased further after 9 hours of ischemia and 2 hours of reperfusion. Light- and electron microscopic findings correlated strongly with the values of muscle fiber viability: lesser viability values represented higher degree of ultrastructural injury while similar viability results corresponded to similar morphological injury. Muscle fiber viability was capable of accurately determining the degree of muscle injury in our rat model. Our method might therefore be useful in clinical settings in the diagnostics of acute ischemic muscle injury
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