669 research outputs found
Extraction Methods and an Investigation of Drosophila Lipids
In earlier work (8) we extracted lipids from dried, macerated Drosophila melanogaster with ether, but later, working with larger quantities of undried flies, we found that most of the phospholipids were autolyzed. Kates' studies (2) led him to suggest n-propanol or isopropanol for lipid extraction (isopropanol was his later choice (6, 7)). Attempting to meet the requirements discussed above, we developed a new and relatively simple method of extraction employing n-propanol (9), or chloroformmethanol (2:1). The latter proved to be a more useful solvent. The method will be described in detail below, with results of an examination of Drosophila lipids
Phospholipides containing amino acids other than serine. I. Detection
In view of the widespread occurrence of the amino acid-containing lipides and the unique course of their metabolism during development of Drosophila, we have carried out extensive investigations concerned with their isolation and chemical nature. The present report is concerned primarily with techniques and procedures developed to insure removal of non-lipide contaminants from preparations of these lipides
Exploring constrained quantum control landscapes
The broad success of optimally controlling quantum systems with external
fields has been attributed to the favorable topology of the underlying control
landscape, where the landscape is the physical observable as a function of the
controls. The control landscape can be shown to contain no suboptimal trapping
extrema upon satisfaction of reasonable physical assumptions, but this
topological analysis does not hold when significant constraints are placed on
the control resources. This work employs simulations to explore the topology
and features of the control landscape for pure-state population transfer with a
constrained class of control fields. The fields are parameterized in terms of a
set of uniformly spaced spectral frequencies, with the associated phases acting
as the controls. Optimization results reveal that the minimum number of phase
controls necessary to assure a high yield in the target state has a special
dependence on the number of accessible energy levels in the quantum system,
revealed from an analysis of the first- and second-order variation of the yield
with respect to the controls. When an insufficient number of controls and/or a
weak control fluence are employed, trapping extrema and saddle points are
observed on the landscape. When the control resources are sufficiently
flexible, solutions producing the globally maximal yield are found to form
connected `level sets' of continuously variable control fields that preserve
the yield. These optimal yield level sets are found to shrink to isolated
points on the top of the landscape as the control field fluence is decreased,
and further reduction of the fluence turns these points into suboptimal
trapping extrema on the landscape. Although constrained control fields can come
in many forms beyond the cases explored here, the behavior found in this paper
is illustrative of the impacts that constraints can introduce.Comment: 10 figure
Quantum Control Landscapes
Numerous lines of experimental, numerical and analytical evidence indicate
that it is surprisingly easy to locate optimal controls steering quantum
dynamical systems to desired objectives. This has enabled the control of
complex quantum systems despite the expense of solving the Schrodinger equation
in simulations and the complicating effects of environmental decoherence in the
laboratory. Recent work indicates that this simplicity originates in universal
properties of the solution sets to quantum control problems that are
fundamentally different from their classical counterparts. Here, we review
studies that aim to systematically characterize these properties, enabling the
classification of quantum control mechanisms and the design of globally
efficient quantum control algorithms.Comment: 45 pages, 15 figures; International Reviews in Physical Chemistry,
Vol. 26, Iss. 4, pp. 671-735 (2007
Direct Observation of the Fourth Star in the Zeta Cancri System
Direct imaging of the zeta Cnc system has resolved the fourth star in the
system, which is in orbit around zeta Cnc C. The presence of the fourth star
has been inferred for many years from irregularities in the motion of star C,
and recently from C's spectroscopic orbit. However, its mass is close to that
of C, making its non-detection puzzling. Observing at wavelengths of 1.2, 1.7,
and 2.2 microns with the adaptive-optics system of the CFHT, we have obtained
images which very clearly reveal star D and show it to have the color of an M2
star. Its brightness is consonant with its being two M stars, which are not
resolved in our observations but are likely to be in a short-period orbit,
thereby accounting for the large mass and the difficulty of detection at
optical wavelengths, where the magnitude difference is much larger. The
positions and colors of all four stars in the system are reported and are
consistent with the most recent astrometric observations.Comment: 7 pages including 3 tables, 1 figure; To appear in PAS
The role of controllability in optimizing quantum dynamics
This paper discusses the important role of controllability played on the
complexity of optimizing quantum mechanical control systems. The study is based
on a topology analysis of the corresponding quantum control landscape, which is
referred to as the optimization objective as a functional of control fields. We
find that the degree of controllability is closely relevant with the ruggedness
of the landscape, which determines the search efficiency for global optima.
This effect is demonstrated via the gate fidelity control landscape of a system
whose controllability is restricted on a SU(2) dynamic symmetry group. We show
that multiple local false traps (i.e., non-global suboptima) exist even if the
target gate is realizable and that the number of these traps is increased by
the loss of controllability, while the controllable systems are always devoid
of false traps.Comment: 13 pages, 3 figure
The landscape of quantum transitions driven by single-qubit unitary transformations with implications for entanglement
This paper considers the control landscape of quantum transitions in
multi-qubit systems driven by unitary transformations with single-qubit
interaction terms. The two-qubit case is fully analyzed to reveal the features
of the landscape including the nature of the absolute maximum and minimum, the
saddle points and the absence of traps. The results permit calculating the
Schmidt state starting from an arbitrary two-qubit state following the local
gradient flow. The analysis of multi-qubit systems is more challenging, but the
generalized Schmidt states may also be located by following the local gradient
flow. Finally, we show the relation between the generalized Schmidt states and
the entanglement measure based on the Bures distance
Quantum control by von Neumann measurements
A general scheme is presented for controlling quantum systems using evolution
driven by non-selective von Neumann measurements, with or without an additional
tailored electromagnetic field. As an example, a 2-level quantum system
controlled by non-selective quantum measurements is considered. The control
goal is to find optimal system observables such that consecutive non-selective
measurement of these observables transforms the system from a given initial
state into a state which maximizes the expected value of a target operator (the
objective). A complete analytical solution is found including explicit
expressions for the optimal measured observables and for the maximal objective
value given any target operator, any initial system density matrix, and any
number of measurements. As an illustration, upper bounds on measurement-induced
population transfer between the ground and the excited states for any number of
measurements are found. The anti-Zeno effect is recovered in the limit of an
infinite number of measurements. In this limit the system becomes completely
controllable. The results establish the degree of control attainable by a
finite number of measurements
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