Input and output in damped quantum systems III: Formulation of damped systems driven by Fermion fields

A comprehensive input-output theory is developed for Fermionic input fields. Quantum stochastic differential equations are developed in both the Ito and Stratonovich forms. The major technical issue is the development of a formalism which takes account of anticommutation relations between the Fermionic driving field and those system operators which can change the number of Fermions within the system

Magnetic Phase Diagrams of Multiferroic Hexagonal RMnO3 (R=Er, Yb, Tm, and Ho)

The magnetic phase diagrams of RMnO3 (R = Er, Yb, Tm, Ho) are investigated up to 14 Tesla via magnetic and dielectric measurements. The stability range of the AFM order below the Neel temperature of the studied RMnO3 extends to far higher magnetic fields than previously assumed. Magnetic irreversibility indicating the presence of a spontaneous magnetic moment is found near 50 K for R=Er, Yb, and Tm. At very low temperatures and low magnetic fields the phase boundary defined by the ordering of the rare earth moments is resolved. The sizable dielectric anomalies observed along all phase boundaries are evidence for strong spin-lattice coupling in the hexagonal RMnO3. In HoMnO3 the strong magnetoelastic distortions are investigated in more detail via magnetostriction experiments up to 14 Tesla. The results are discussed based on existing data on magnetic symmetries and the interactions between the Mn-spins, the rare earth moments, and the lattice.Comment: 23 pages, 16 figures, to be published in JMR's Aug. focus issue on multiferroic

Magnetic phase diagrams of the Kagome staircase compound Co3V2O8

At zero magnetic field, a series of five phase transitions occur in Co3V2O8. The Neel temperature, TN=11.4 K, is followed by four additional phase changes at T1=8.9 K, T2=7.0 K, T3=6.9 K, and T4=6.2 K. The different phases are distinguished by the commensurability of the b-component of its spin density wave vector. We investigate the stability of these various phases under magnetic fields through dielectric constant and magnetic susceptibility anomalies. The field-temperature phase diagram of Co3V2O8 is completely resolved. The complexity of the phase diagram results from the competition of different magnetic states with almost equal ground state energies due to competing exchange interactions and frustration.Comment: Proceedings of the 2007 Conference on Strongly Correlated Electron Systems, 2 pages, 2 figure

Thermal expansion and pressure effect in MnWO4

MnWO4 has attracted attention because of its ferroelectric property induced by frustrated helical spin order. Strong spin-lattice interaction is necessary to explain ferroelectricity associated with this type of magnetic order.We have conducted thermal expansion measurements along the a, b, c axes revealing the existence of strong anisotropic lattice anomalies at T1=7.8 K, the temperature of the magnetic lock-in transition into a commensurate low-temperature (reentrant paraelectric) phase. The effect of hydrostatic pressure up to 1.8 GPa on the FE phase is investigated by measuring the dielectric constant and the FE polarization. The low- temperature commensurate and paraelectric phase is stabilized and the stability range of the ferroelectric phase is diminished under pressure.Comment: 2 pages, 3 figures. SCES conference proceedings, houston, TX, 2007. to be published in Physica

Characterization of an INVS Model IV Neutron Counter for High Precision (γ,n\gamma,n) Cross-Section Measurements

A neutron counter designed for assay of radioactive materials has been adapted for beam experiments at TUNL. The cylindrical geometry and 60% maximum efficiency make it well suited for ($\gamma,n$) cross-section measurements near the neutron emission threshold. A high precision characterization of the counter has been made using neutrons from several sources. Using a combination of measurements and simulations, the absolute detection efficiency of the neutron counter was determined to an accuracy of $\pm$ 3% in the neutron energy range between 0.1 and 1 MeV. It is shown that this efficiency characterization is generally valid for a wide range of targets.Comment: 22 pages, 13 figure

Altered renal hemodynamics and impaired myogenic responses in the fawn-hooded rat

The present study examined whether an abnormality in the myogenic response of renal arterioles that impairs autoregulation of renal blood flow (RBF) and glomerular capillary pressure (PGC) contributes to the development of renal damage in fawn-hooded hypertensive (FHH) rats. Autoregulation of whole kidney, cortical, and medullary blood flow and PGC were compared in young (12 wk old) FHH and fawn-hooded low blood pressure (FHL) rats in volume-replete and volume-expanded conditions. Baseline RBF, cortical and medullary blood flow, and PGC were significantly greater in FHH than in FHL rats. Autoregulation of renal and cortical blood flow was significantly impaired in FHH rats compared with results obtained in FHL rats. Myogenically mediated autoregulation of PGC was significantly greater in FHL than in FHH rats. PGC rose from 46 +/- 1 to 71 +/- 2 mmHg in response to an increase in renal perfusion pressure from 100 to 150 mmHg in FHH rats, whereas it only increased from 39 +/- 2 to 53 +/- 1 mmHg in FHL rats. Isolated perfused renal interlobular arteries from FHL rats constricted by 10% in response to elevations in transmural pressure from 70 to 120 mmHg. In contrast, the diameter of vessels from FHH rats increased by 15%. These results indicate that the myogenic response of small renal arteries is altered in FHH rats, and this contributes to an impaired autoregulation of renal blood flow and elevations in PGC in this strain

Imaging of the ejection process of nanosecond laser-induced forward transfer of gold

Laser-induced forward transfer is a direct-write process suitable for high precision 3D printing of several materials. However, the driving forces related to the ejection mechanism of the donor ma-terial are still under debate. So far, most of the experimental studies of nanosecond LIFT, are based on post process analysis of either the donor layer and/or the deposits, which were transferred to the receiving substrate. To gain further insights into the ejection dynamics, this article presents results of a series of imaging experiments of the release process of nanosecond LIFT of a 200 nm thick gold donor layer. Images were obtained using a setup which consists of two dual-shutter cameras. Both cameras were combined with a 50× long-distance microscope and used to capture coaxial and side-view images of the ejection process. Bright field illumination of the scene was accomplished by a 6 ns dual-cavity laser source. For laser fluence just above the transfer threshold, the formation of a jet and the subsequent release of a single droplet was observed. The droplet diameter was esti-mated to be about 2 μm. Analysis of the coaxial images indicates the emission of a spectral broad range light which was identified as thermal radiation

Droplet ejection in laser-induced forward transfer: mechanism for droplet fragmentation

Laser-induced forward transfer is a direct-write method suitable for precision printing of various materials. However, occasional defects (i.e. contamination of the receiver due to the impact of multiple small droplets instead of a single droplet) hamper a widespread application of this method. As the ejection mechanism has not been visualized in detail, the cause of these defects is not understood as yet. Therefore, this article presents an experimental study on the ejection process mechanisms of copper-based picosecond laser-induced forward transfer. Images were obtained using bright field illumination by a 6 ns pulsed laser and a 50× long-distance microscope objective. For laser fluences just above the transfer-threshold, the release of a single droplet is frequently (97%) observed. The typical droplet radius in these cases is estimated to be 3 μm. However, images acquired at a later time in time show multiple droplets in the majority (86%) of the observations. The droplet fragments usually follow the main droplet. Two mechanisms to explain these fragments are proposed: i) break-up of “threads” between the donor layer and the ejected droplet; ii) contraction of the ejected droplet. As the phase of the ejected copper is not identified completely, the exact mechanism is not yet known and will be subject of further research

Optimizing cell viability in dropletbased cell deposition

Biofabrication commonly involves the use of liquid droplets to transport cells to the printed structure. However, the viability of the cells after impact is poorly controlled and understood, hampering applications including cell spraying, inkjet bioprinting, and laser-assisted cell transfer. Here, we present an analytical model describing the cell viability after impact as a function of the cell-surrounding droplet characteristics. The model connects (1) the cell survival as a function of cell membrane elongation, (2) the membrane elongation as a function of the cell-containing droplet size and velocity, and (3) the substrate properties. The model is validated by cell viability measurements in cell spraying, which is a method for biofabrication and used for the treatment of burn wounds. The results allow for rational optimization of any droplet-based cell deposition technology, and we include practical suggestions to improve the cell viability in cell spraying