CBETA: First Multipass Superconducting Linear Accelerator with Energy Recovery.

Energy recovery has been achieved in a multipass linear accelerator, demonstrating a technology for more compact particle accelerators operating at higher currents and reduced energy consumption. Energy delivered to the beam during the first four passes through the accelerating structure was recovered during four subsequent decelerating passes. High-energy efficiency was achieved by the use of superconducting accelerating cavities and permanent magnets. The fixed-field alternating-gradient optical system used for the return loop successfully transported electron bunches of 42, 78, 114, and 150 MeV in a common vacuum chamber. This new kind of accelerator, an eight-pass energy recovery linac, has the potential to accelerate much higher current than existing linear accelerators while maintaining small beam dimensions and consuming much less energy per electron.

High-Brightness Continuous-Wave Electron Beams from Superconducting Radio-Frequency Photoemission Gun.

Continuous-wave photoinjectors operating at high accelerating gradients promise to revolutionize many areas of science and applications. They can establish the basis for a new generation of monochromatic x-ray free electron lasers, high-brightness hadron beams, or a new generation of microchip production. In this Letter we report on the record-performing superconducting rf electron gun with CsK_{2}Sb photocathode. The gun is generating high charge electron bunches (up to 10 nC/bunch) and low transverse emittances, while operating for months with a single photocathode. This achievement opens a new era in generating high-power beams with a very high average brightness.

Experimental Demonstration of Hadron Beam Cooling Using Radio-Frequency Accelerated Electron Bunches.

Cooling of beams of gold ions using electron bunches accelerated with radio-frequency systems was recently experimentally demonstrated in the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. Such an approach is new and opens the possibility of using this technique at higher energies than possible with electrostatic acceleration of electron beams. The challenges of this approach include generation of electron beams suitable for cooling, delivery of electron bunches of the required quality to the cooling sections without degradation of beam angular divergence and energy spread, achieving the required small angles between electron and ion trajectories in the cooling sections, precise velocity matching between the two beams, high-current operation of the electron accelerator, as well as several physics effects related to bunched-beam cooling. Here we report on the first demonstration of cooling hadron beams using this new approach.

A multiscale in silico model of endothelial to mesenchymal transformation in a tumor microenvironment.

Endothelial to mesenchymal transformation (EndMT) is a process in which endothelial cells gain a mesenchymal-like phenotype in response to mechanobiological signals that results in the remodeling or repair of underlying tissue. While initially associated with embryonic development, this process has since been shown to occur in adult tissue remodeling including wound healing, fibrosis, and cancer. In an attempt to understand the role of EndMT in cancer progression and metastasis, we present a multiscale, three-dimensional, in silico model. The model couples tissue level phenomena such as extracellular matrix remodeling, cellular level phenomena such as migration and proliferation, and chemical transport in the tumor microenvironment to mimic in vitro tissue models of the cancer microenvironment. The model is used to study the presence of EndMT-derived activated fibroblasts (EDAFs) and varying substrate stiffness on tumor cell migration and proliferation. The simulations accurately model the behavior of tumor cells under given conditions. The presence of EDAFs and/or an increase in substrate stiffness resulted in an increase in tumor cell activity. This model lays the foundation of further studies of EDAFs in a tumor microenvironment on a cellular and subcellular physiological level.

An array of virtual Frisch-grid CdZnTe detectors and a front-end application-specific integrated circuit for large-area position-sensitive gamma-ray cameras.

We developed a robust and low-cost array of virtual Frisch-grid CdZnTe detectors coupled to a front-end readout application-specific integrated circuit (ASIC) for spectroscopy and imaging of gamma rays. The array operates as a self-reliant detector module. It is comprised of 36 close-packed 6 × 6 × 15 mm(3) detectors grouped into 3 × 3 sub-arrays of 2 × 2 detectors with the common cathodes. The front-end analog ASIC accommodates up to 36 anode and 9 cathode inputs. Several detector modules can be integrated into a single- or multi-layer unit operating as a Compton or a coded-aperture camera. We present the results from testing two fully assembled modules and readout electronics. The further enhancement of the arrays' performance and reduction of their cost are possible by using position-sensitive virtual Frisch-grid detectors, which allow for accurate corrections of the response of material non-uniformities caused by crystal defects.

Effective environments: preparation of stationary states with inverse temperature ranging from positive to negative values.

In this paper, we discuss how effective environments incorporating periodic measurements can be used to prepare a two-level system (TLS) in almost arbitrary thermal states: Concretely, we study a TLS coupled to a spin environment, the magnetization of which is measured periodically. In ensemble average these measurements cause a relaxation of the TLS into a thermal (diagonal) state. By adjusting the time between the measurements and the detuning of the environmental spins, the creation of very low temperatures as well as inversion becomes possible. Our analytical results derived for large environments are numerically shown to be valid even for quite small environments, down to only a few spins.

Operational approach to fluctuations of thermodynamic variables in finite quantum systems.

In this paper we present a quantum approach to the old problem of temperature fluctuations. We start by observing that according to quantum thermodynamics, fluctuations of intensive parameters like temperature cannot exist. Furthermore, such parameters are not observables, so their estimation has to be done indirectly. The respective temperature estimate based on quantum measurements of the energy is shown to fluctuate according to the well-known formula ΔT(2)=k(B)T(2)/C, but only within a certain temperature range and if the system is not too small. We also calculate the fourth-order correction term, becoming important at higher temperatures. Finally we illustrate our results with a concrete model of n spins.

Lasing process in a closed bipartite quantum system: a thermodynamical analysis.

Closed weakly bound bipartite quantum systems typically exhibit relaxation behavior with respect to the smaller subsystem. Here, we investigate a model composed of a finite spin network with one interfacing spin being coupled to a single electromagnetic field mode via the Jaynes-Cummings interaction. The initial pure state of the system can be chosen such that the resulting thermodynamical relaxation process is lasing/nonlasing relaxation or energy back flow from the field mode. We examine the properties of the field mode with quantum optical methods. During the lasing process, the field mode is in a phase-diffused Glauber state with no optical coherence. The thermodynamical analysis of our system is consistent with this finding: The total energy exchanged between both subsystems is found to be heat only. Yet the mapping of this function onto a thermodynamic heat engine appears to be of limited value.

Quantum optical thermodynamic machines: lasing as relaxation.

Motivated by the growing interest in the nanophysics and the field of quantum thermodynamics we study an open quantum system consisting of two spatially separated two-level atoms (spins) coupled to a quantum oscillator (resonator field mode). There is no external driving. The spins of different energy splittings are each linked to a heat bath with different temperature. We find that the temperature gradient imposed on the system together with the oscillator operating as a kind of work reservoir makes this system act as a thermodynamic machine, in particular, as a heat engine (laser). We analyze the properties of the resulting resonator field and of the engine functionality. For the latter problem we use recently developed definitions of heat flux and power as well as a test, in which the resulting field is used as an input for a heat pump.

Quantum approach to a derivation of the second law of thermodynamics.

We reinterpret the microcanonical conditions in the quantum domain as constraints for the interaction of the "gas subsystem" under consideration and its environment ("container"). The time average of a purity measure is found to equal the average over the respective path in Hilbert space. We then show that for typical (degenerate or nondegenerate) thermodynamical systems almost all states within the allowed region of Hilbert space have a local von Neumann entropy S close to the maximum and a purity P close to its minimum, respectively. Typically, thermodynamical systems should obey the second law.

Influence of iron on growth, production of siderophore compounds, membrane proteins, and lipase activity in Acinetobacter calcoaceticus BD 413.

Acinetobacter calcoaceticus BD413 was examined for production of siderophores and iron-repressible outer membrane proteins following growth in iron-restricted media. The iron-scavenging phenotype was associated with the secretion of iron-repressible catechol and the induction of a group of six outer membrane proteins with molecular weights ranging from 34 to 85 kDa. The amount of catechol produced was dependent on medium composition and iron stringency. The relation between iron limitation and lipase production was studied at the level of lipA transcription and extracellular lipase activity. In minimal medium, iron limitation slightly affected lipA expression but decreased exo-lipase activity significantly. However, if iron limitation and rich nitrogen sources were simultaneously present in the culture media, the production of lipase was increased approximately 4 times.

Effect of magnesium ions on fermentative and respirative functions in Pichia stipitis under oxygen-restricted growth.

Mg2+ level affected growth, xylitol and ethanol production by P. stipitis grown under microaerophilic conditions. Low Mg2+ level (1 mM) directed the C flux from ethanol to xylitol, with no effect on xylose consumption rate. The addition of pyrazole, an alcohol dehydrogenase (ADH) inhibitor, had the same effect, even in conditions of Mg2+ excess (4 mM), indicating a negative interaction between ADH and Mg2+ ions (p << 0.01). Cells grown either with pyrazole or Mg limitation increased their intracellular NADH concentration about 3 times, but displayed no significant differences in ADH specific activities (1,000 U/mg protein, +/- 10%). In contrast, no interaction was measured between Mg and antimycin A, excluding the possibility that Mg2+ limitation interferes with respiration.

Quantum control by compensation of quantum fluctuations.

We show that the influence of quantum fluctuations in the electromagnetic field vacuum on a two level atom can be measured and consequently compensated by balanced homodyne detection and a coherent feedback field. This compensation suppresses the decoherence associated with spontaneous emissions for a specific state of the atomic system allowing complete control of the coherent state of the system.