Calculating the bound spectrum by path summation in action-angle variables

The density of states n(E) is calculated for a bound system whose classical motion is integrable, starting from an expression in terms of the trace of the time-dependent Green function. The novel feature is the use of action-angle variables. This has the advantages that the trace operation reduces to a trivial multiplication and the dependence of n(E) on all classical closed orbits with different topologies appears naturally. The method is contrasted with another, not applicable to integrable systems except in special cases, in which quantization arises from a single closed orbit which is assumed isolated and the trace taken by the method of stationary phase.

Synthesis, Structure, and Transformation Studies in a Family of Inorganic-Organic Hybrid Framework Structures Based on Indium

Eight new open-framework inorganic-organic hybrid compounds based on indium have been synthesized employing hydrothermal methods. All of the compounds have InO6, C2O4, and HPO3/HPO4/SO4 units connected to form structures of different dimensionality Thus, the compounds have zero- (I), two- (II, III, IV, V, VII, and VIII), and three-dimensionally (VI) extended networks. The formation of the first zero-dimensional hybrid compound is noteworthy In addition, concomitant polymorphic structures have been observed in the present study. The molecular compound, I, was found to be reactive, and the transformation studies in the presence of a base (pyridine) give rise to the polymorphic structures of II and III, while the addition of an acid (H3PO3) gives rise to a new indium phosphite with a pillared layer structure (T1). Preliminary density functional theory calculations suggest that the stabilities of the polymorphs are different, with one of the forms (II) being preferred over the other, which is consistent with the observed experimental behavior. The oxalate units perform more than one role in the present structures. Thus, the oxalate units connect two In centers to satisfy the coordination requirements as well as to achieve charge balance in compounds II, IV, and VI. The terminal oxalate units observed in compounds I, IV, and V suggest the possibility of intermediate structures. Both in-plane and out-of-plane connectivity of the oxalate units were observed in compound VI. The 31 compounds have been characterized by powder X-ray diffraction, IR spectroscopy, thermogravimetric analysis, and P-31 NMR studies.

Phenotypic and Functional Characterization of Human Mammary Stem/Progenitor Cells in Long Term Culture

Background: Cancer stem cells exhibit close resemblance to normal stem cells in phenotype as well as function. Hence, studying normal stem cell behavior is important in understanding cancer pathogenesis. It has recently been shown that human breast stem cells can be enriched in suspension cultures as mammospheres. However, little is known about the behavior of these cells in long-term cultures. Since extensive self-renewal potential is the hallmark of stem cells, we undertook a detailed phenotypic and functional characterization of human mammospheres over long-term passages. Methodology: Single cell suspensions derived from human breast `organoids' were seeded in ultra low attachment plates in serum free media. Resulting primary mammospheres after a week (termed T1 mammospheres) were subjected to passaging every 7th day leading to the generation of T2, T3, and T4 mammospheres. Principal Findings: We show that primary mammospheres contain a distinct side-population (SP) that displays a CD24(low)/CD44(low) phenotype, but fails to generate mammospheres. Instead, the mammosphere-initiating potential rests within the CD44(high)/CD24(low) cells, in keeping with the phenotype of breast cancer-initiating cells. In serial sphere formation assays we find that even though primary (T1) mammospheres show telomerase activity and fourth passage T4 spheres contain label-retaining cells, they fail to initiate new mammospheres beyond T5. With increasing passages, mammospheres showed an increase in smaller sized spheres, reduction in proliferation potential and sphere forming efficiency, and increased differentiation towards the myoepithelial lineage. Significantly, staining for senescence-associated beta-galactosidase activity revealed a dramatic increase in the number of senescent cells with passage, which might in part explain the inability to continuously generate mammospheres in culture. Conclusions: Thus, the self-renewal potential of human breast stem cells is exhausted within five in vitro passages of mammospheres, suggesting the need for further improvisation in culture conditions for their long-term maintenance.

On the coalescence of twisted flux tubes

We study the problem of the coalescence of twisted flux tubes by assuming that the azimuthal field lines reconnect at a current sheet during the coalescence process and everywhere else the magnetic field is frozen in the fluid. We derive relations connecting the topology of the coalesced flux tube with the topologies of the initial flux tubes, and then obtain a structure equation for calculating the field configuration of the coalesced flux tube from the given topology. Some solutions for the two extreme cases of low-β plasma and high-β plasma are discussed. The coalesced flux tube has less twist than the initial flux tube. Magnetic helicity is found to be exactly conserved during the coalescence, but the assumptions in the model put a constraint on the energy dissipation so that we do not get a relaxation to the minimum-energy Taylor state in the low-β case. It is pointed out that the structure equation connecting the topology and the equilibrium configuration is quite general and can be of use in many two-dimensional flux tube problems.

1H NMR study of internal motions and quantum rotational tunneling in (CH3)4NGeCl3

(CH3)4NGeCl3 is prepared, characterized and studied using 1H NMR spin lattice relaxation time and second moment to understand the internal motions and quantum rotational tunneling. Proton second moment is measured at 7 MHz as function of temperature in the range 300-77 K and spin lattice relaxation time (T1) is measured at two Larmor frequencies, as a function of temperature in the range 270-17 K employing a homemade wide-line/pulsed NMR spectrometers. T1 data are analyzed in two temperature regions using relevant theoretical models. The relaxation in the higher temperatures (270-115 K) is attributed to the hindered reorientations of symmetric groups (CH3 and (CH3)4N). Broad asymmetric T1 minima observed below 115 K down to 17 K are attributed to quantum rotational tunneling of the inequivalent methyl groups.

On self-interacting oligoribonucleotides. I. Absorption and optical rotatory dispersion of 2′-5′- and 3′-5′-oligoguanylic acids

A series of 2′-5′-oligoguanylic acids are prepared by reacting G(cyclic)p with takadiastase T1 ribonuclease and separating the products chromatographically. The 3′-5′-oligoguanylic acids are obtained by separating the products of alkaline degradation of 3′-5′-poly(G). The optical rotatory dispersion and hypochromism of both 2′-5′- and 3′-5′-oligoguanylic acids are studied at two different pH. The optical rotatory dispersion spectrum of 2′-5′-GpG is significantly different from that of 3′-5′-GpG. The magnitude of rotation of the long-wavelength peak of 2′-5′-GpG is larger than that of 3′-5′-GpG. This finding contradicts the explanation that the extra stability and more intense circular dichroism band of other 3′-5′-dinucleoside monophosphates is due to H-bond formation between 2′-OH and either the base or the phosphate oxygen. The end phosphate group has a marked effect on the spectrum of GpG between 230 and 250 mμ. In addition the optical rotatory dispersion spectra of 2′-5′ exhibit strong pH, temperature, and solvent dependence between 230 and 250 mμ. ΔH and AS for order ⇌ disorder transition is estimated to be 9.7 kcal/mole and 35.2 eu, respectively. The optical rotatory dispersion spectra of guanine-rich oligoribonucleotides, GpGpC, GpGpU, GpGpGpC, and GpGpGpU are compared to the calculated optical rotatory dispersion from the semiempirical expression of Cantor and Tinoco, using measured optical rotatory dispersion of dimers. Contrary to previous studies, agreement is found not at all satisfactory. However, optical rotatory dispersion of 3′-5′-GpGpGpC and GpGpGpU can be estimated from the semiempirical expression, if a next-nearest interaction parameter is introduced empirically. Such interaction parameter can be calculated from the measured properties of trinucleotide sequences like GpGpG, GpGpC, and GpGpU, assuming that only the nearest-neighbor interaction is important. The optical rotatory dispersion of single-stranded poly(G) is also predicted. The importance of syn-anti equilibrium and next-nearest-neighbor interaction in oligoguanylic acids is suggested as a probable explanation.

A Survey on Cascaded Multilevel Inverters

Cascaded multilevel inverters synthesize a medium-voltage output based on a series connection of power cells which use standard low-voltage component configurations. This characteristic allows one to achieve high-quality output voltages and input currents and also outstanding availability due to their intrinsic component redundancy. Due to these features, the cascaded multilevel inverter has been recognized as an important alternative in the medium-voltage inverter market. This paper presents a survey of different topologies, control strategies and modulation techniques used by these inverters. Regenerative and advanced topologies are also discussed. Applications where the mentioned features play a key role are shown. Finally, future developments are addressed.

A unified model for auxiliary switch commutated DC-DC converters

A novel ZVS auxiliary switch commutated variation for all DGDC converter topologies has been proposed in 2006. With proper designation of the circuit variables (throw current I and the pole voltage V), all these converters are seen to be governed by an identical set of equations. With idealized switches, the steady-state performance is obtainable in an analytical form. The conversion ratio of the converter topologies is obtained. A generalized equivalent circuit emerges for all these converters from the steady-state conversion ratio. It also provides a dynamic model as well. With these generalized steady-state equivalent circuits, small signal analysis of these converters may be carried out readily. It enables one to use the familiar state space averaged results of the standard PWM DGDC converters for the resonant counterparts. Th dc and ac models reveals that dc and low frequency behaviour of the proposed family of converters is similiar to that of its PWM parent

A generalized Linear Programming based approach to optimal divisible load scheduling

In this paper we propose a general Linear Programming (LP) based formulation and solution methodology for obtaining optimal solution to the load distribution problem in divisible load scheduling. We exploit the power of the versatile LP formulation to propose algorithms that yield exact solutions to several very general load distribution problems for which either no solutions or only heuristic solutions were available. We consider both star (single-level tree) networks and linear daisy chain networks, having processors equipped with front-ends, that form the generic models for several important network topologies. We consider arbitrary processing node availability or release times and general models for communication delays and computation time that account for constant overheads such as start up times in communication and computation. The optimality of the LP based algorithms is proved rigorously.

Determination of distances of sugar protons from Mn2+ in concanavalin A

1H NMR spin-lattice relaxation time (T1) measurements have been carried out with various sugars, viz. methyl alpha-D-glucopyranoside (alpha-MeGluP), methyl beta-D-lucopyranoside (beta-MeGluP), methyl alpha--annopyranoside (alpha-MeManP), maltose (4-O-alpha-D-glucopyranosyl--glucose), nigerose (3-O-alpha-D-glucopyranosyl-D-glucose), p-nitrophenyl alpha-maltoside (PNP-alpha-maltoside) and p-nitrophenyl beta-maltoside (PNP-beta-maltoside) to determine the distances of sugar protons from Mn2+ in concanavalin A (Con A). With a rotational correlation time of 1.58 x 10(-10) s determined, distances were calculated using Solomon-Bloembergen equation. The data obtained indicated differences in disposition of different groups in the binding site of Con A. An average value of about 10 A was obtained for the distances of sugar protons from Mn2+ in Con A. In the case of mono and disaccharides, the non-reducing end sugar unit was found to be closer to Mn2+ than the reducing end one.

A Simple Five-Level Inverter Topology for Induction Motor Drive Using Conventional Two-Level Inverters and Flying Capacitor Technique

This paper proposes a new five-level inverter topology for open-end winding induction motor (IM) drive. The popular existing circuit configurations for five-level inverter include the NPC inverter and flying capacitor topologies. Compared to the NPC inverter, the proposed topology eliminates eighteen clamping diodes having different voltage ratings in the present circuit. Moreover it requires only one capacitor bank per phase, whereas flying capacitor schemes for five level topologies require six capacitor banks per phase. The proposed topology is realized by feeding the phase winding of an open-end induction motor with two-level inverters in series with flying capacitors. The flying capacitor voltages are balanced using the switching state redundancy for full modulation range. The proposed inverter scheme is capable of producing two-level to five-level pulse width modulated voltage across the phase winding depending on the modulation range. Additionally, in case of any switch failure in the flying capacitor connection, the proposed inverter topology can be operated as a three-level inverter for full modulation range. The proposed scheme is experimentally verified on a four pole, 5hp induction motor drive.

Photochemical, photophysical, and theoretical studies on cyclobutanethiones..alpha.-Cleavage reactions

Photophysics and photochemistry of cyclobutanethiones 1-5 have been studied with the view to generalize the a-cleavage reactions of cyclobutanethiones. The above cyclobutanethiones possess a unit intersystem crossing efficiency from S1 to T1, a high self-quenching rate (-4 X lo9 M-' s-'), and a short triplet lifetime (<0.50 ws). Photolysis of 1-5 yields in benzene a product resulting from 1,3-transposition and in methanol two cyclic thioacetals.The origin of these products is traced to the triplet excited state. A mechanistic scheme involving a-cleavage as the primary photoprocess and diradicals and thiacarbenes as intermediates has been formulated to rationalize the formation of thioacetals and rearranged products. The proposed mechanistic scheme is supported by UHF MIND013 calculations performed on four model systems, cyclobutanethiones and 1,3-cyclobutanedithiones 18-21. These calculations indicate that formation of diradical is favored thermodynamically and kinetically for systems analogous to 19 and 21, while rearrangement to thiacarbene is likely only for those similar to 21.

Recent Advances and Industrial Applications of Multilevel Converters

Multilevel converters have been under research and development for more than three decades and have found successful industrial application. However, this is still a technology under development, and many new contributions and new commercial topologies have been reported in the last few years. The aim of this paper is to group and review these recent contributions, in order to establish the current state of the art and trends of the technology, to provide readers with a comprehensive and insightful review of where multilevel converter technology stands and is heading. This paper first presents a brief overview of well-established multilevel converters strongly oriented to their current state in industrial applications to then center the discussion on the new converters that have made their way into the industry. In addition, new promising topologies are discussed. Recent advances made in modulation and control of multilevel converters are also addressed. A great part of this paper is devoted to show nontraditional applications powered by multilevel converters and how multilevel converters are becoming an enabling technology in many industrial sectors. Finally, some future trends and challenges in the further development of this technology are discussed to motivate future contributions that address open problems and explore new possibilities.

Quasicrystalline and related crystalline phases in a rapidly solidified 2024-2Li aluminium alloy

The formation and decomposition of quasicrystalline and crystalline phases in as-rapidly solidified and annealed commercial AISI 2024 aluminum alloy containing 2 wt% Li have been investigated by detailed transmission electron microscopy, including a combination of bright field and dark field imaging, selected area diffraction pattern analysis and energy dispersive X-ray microanalysis. The microstructure of as-melt spun 2024-2Li consists of alpha-Al cells, containing small coherent delta' precipitates, and particles or a continuous network of the icosahedral phase at the cell boundaries. After annealing at 300-degrees-C, the intercellular particles of the icosahedral phase coarsen progressively and assume a more faceted shape; after annealing at 400-degrees-C, particles of the decagonal and crystalline O phases precipitate heterogeneously on preexisting particles of the icosahedral phase; and after annealling at 500-degrees-C, the icosahedral and decagonal phases dissolve completely, and small particles of the crystalline O phase remain together with newly precipitated plates of the T1 phase. The icosahedral phase in melt spun and melt spun/annealed 2024-2Li belongs to the Al6CuLi3 class of icosahedral phases, with a quasilattice constant of 0.51 nm, a stoichiometry of (Al, Si)6(Cu, Mn, Fe) (Li, Mg)3 and an average composition of Al-24.1 at.% Cu-6.4 at.% Mg-1.7 at.% Si-0.3 at.% Mn-0.5 at.% Fe as-melt spun and Al-21.9 at.% Cu-6.3 at.% Mg-1.0 at.% Si-0.5 at.% Fe as-heat-treated. The decagonal phase in melt spun/annealed 2024-2Li belongs to the Al4Mn class of decagonal phases, with a periodicity of 1.23 nm along the 10-fold symmetry axis, a stoichiometry of Al3(Cu, Mn, Fe) and an average composition of Al-10.3 at.% Cu-13.8 at.% Mn-2.3 at.% Fe. The crystalline O phase in melt spun/annealed 2024-2Li has an orthorhombic structure with lattice parameters of a = 2.24 nm, b = 2.35 nm and c = 1.23 nm, a stoichiometry of Al3(Cu, Mn, Fe) and an average composition of Al-11.0 at.% Cu-14.8 at.% Mn-3.9 at.% Fe. Detailed analysis of selected area diffraction patterns shows a close similarity between the icosahedral, decagonal and crystalline O phases in melt spun and melt spun/annealed 2024-2Li. In particular, the decagonal phase and crystalline O phases have a similar composition, and exhibit an orientation relationship which can be expressed as: [GRAPHICS] suggesting that the orthorhombic O phase is an approximant structure for the decagonal phase.

Single‐gate deep level transient spectroscopy technique

A new deep level transient spectroscopy technique is suggested which allows the deep level parameters to be obtained from a single temperature scan. Using large ratio t2/t1 of the measurement gate positions t1 and t2 and analyzing the steep high‐temperature side of the peak, it is demonstrated that the deep level activation energy can be determined with high accuracy.