So-called Reversal Research Articles

Theory of the hysteresis loop in ferromagnets

We consider three mechanisms of hysteresis phenomena in alternating magnetic field: the domain wall motion in a random medium, the nucleation and the retardation of magnetization due to slow (critical) fluctuations. We construct quantitative theory for all these processes. The hysteresis is characterized by two dynamic threshold fields, by coercive field and by the so-called reversal field. Their ratios to the static threshold field is shown to be function of two dimensionless variables constituted from the frequency and amplitude of the ac field as well as from some characteristics of the magnet. The area and the shape of the hysteresis loop are found. We consider different limiting cases in which power dependencies are valid. Numerical simulations show the domain wall formation and propagation and confirm the main theoretical predictions. Theory is compared with available experimental data.

Complex Kinetics of Desorption and Diffusion. Field Reversal Study of K Excited-State Desorption from Graphite Layer Surfaces

Rapid molecular-beam kinetics data are reported of thermal desorption of K atoms from pyrolytic graphite films over the temperature range 960−1800 K. By using the so-called field reversal method (FR), the kinetics of desorption is studed at time constants down to the microsecond range, where bulk diffusion becomes rate-limiting. The neutral and ionic desorption rates are measured and shown to contain both a primary as well as a secondary rate. These measurements are combined with data on the steady-state and FR peak signals, revealing several states of K on the surface, similar to the previously studied case of Cs on pyrolytic graphite. Two covalently bound states σ4p and σ3d exist, which are 4.30 and 4.40 eV, respectively, below the corresponding atomic configurations 4p (a 2P° term) and 3d (a 2D term) outside the surface. An ionic state is also found, which is 2.0 eV below the corresponding desorbed ion K+ (with the electron at the Fermi level). The 4s and 5s states do not correlate with stable adsorbed states. The apparent neutral rate of desorption is only slowly temperature dependent in the range 960−1550 K, with a primary (fast) rate constant of the order of 300 s-1 and a secondary (slow) rate of 1−10 s-1. This is due to interconversion processes involving diffusion on the surface. In the range 1550−1760 K, processes with activation energies up to 6.07 eV and preexponential factors up to 1021 s-1 are observed for both the fast and the slow rates. Such large preexponential factors are indicative of thermal electronic excitation processes, implying a direct switch to a Rydberg state on the surface. The thermal emission and desorption of alkali atoms in Rydberg states is possible by two main mechanisms: by direct emission from the bulk into high Rydberg states over a thermal barrier of 7.4 eV and by excitation from the covalent states that are transferred to Rydberg states in collisions with the surface.

302 Circumvention of multidrug resistance

Two members of the superfamily of ABC transport proteins, Mr 170.000 PGP and Mr 190.000 MRP, have been identified as multidrug resistance genes. Both genes can act as cellular efflux pumps for natural product anticancer drugs, like anthracyclines, Vinca alkaloids, and epipodophyl-lotoxins. Pgp and MRP are expressed in a variety of tumours, including haematological malignancies. Pharmacological intervention by competitive inhibition of PGP and MRP has been studied in vitro, and clinical studies have been performed with the aim to circumvent (primarily PGP-mediated) MDR. In summary, these attempts have not been very successful, so far, in solid tumours (e.g. kidney and colon cancer) with de novo expression of PGP. For haematological malignancies the results obtained encouraged randomized phase III trials (which are ongoing). The effects of the so-called reversal agents on clinical tumour responses seen in pilot studies, are likely due to specific inhibition of PGP in tumour cells and to altered pharmacokinetics of the cytotoxic drugs. The general idea is that more effective and less toxic reversal agents are needed for clinical trials. However, mdr-knockout mice appeared to be extremely sensitive for xenobiotics. Thus, upon clinical use of highly effective, second generation reversal agents, altered (life-threatening) toxicity profiles should be anticipated. Two members of the superfamily of ABC transport proteins, Mr 170.000 PGP and Mr 190.000 MRP, have been identified as multidrug resistance genes. Both genes can act as cellular efflux pumps for natural product anticancer drugs, like anthracyclines, Vinca alkaloids, and epipodophyl-lotoxins. Pgp and MRP are expressed in a variety of tumours, including haematological malignancies. Pharmacological intervention by competitive inhibition of PGP and MRP has been studied in vitro, and clinical studies have been performed with the aim to circumvent (primarily PGP-mediated) MDR. In summary, these attempts have not been very successful, so far, in solid tumours (e.g. kidney and colon cancer) with de novo expression of PGP. For haematological malignancies the results obtained encouraged randomized phase III trials (which are ongoing). The effects of the so-called reversal agents on clinical tumour responses seen in pilot studies, are likely due to specific inhibition of PGP in tumour cells and to altered pharmacokinetics of the cytotoxic drugs. The general idea is that more effective and less toxic reversal agents are needed for clinical trials. However, mdr-knockout mice appeared to be extremely sensitive for xenobiotics. Thus, upon clinical use of highly effective, second generation reversal agents, altered (life-threatening) toxicity profiles should be anticipated.

A Race Divided: The Indian Westerns of John Ford

Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Cite Icon Cite Search Site Citation Angela Aleiss; A Race Divided: The Indian Westerns of John Ford. American Indian Culture and Research Journal 1 January 1994; 18 (3): 167–186. doi: https://doi.org/10.17953/aicr.18.3.e82817h037185828 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest Search

Pulsed, gridded electron reversal ionizer

The design and performance of a new-type source of negative ions is presented. This device retains the idea of the so-called reversal electron attachment detector [READ, M. T. Bernius and A. Chutjian, J. Appl. Phys. 66, 2783 (1989)] to produce low-energy electrons by reversing electron trajectories at an electrode. Electrons are produced in the present device by several ribbon filaments that surround a cylindrical wire grid. They are accelerated through the grid, then decelerated to zero, or near-zero velocity at the surface of a tube. The tube (anode) is perforated with small holes through which effuse the target molecules. Electrons attach to form either parent and/or fragment negative ions. Attachment takes place at a location above the anode corresponding to a match between the electron energy and the attachment resonance energy. Negative ions are pulsed out of the attachment region and focused onto the entrance plane of a quadrupole mass selector. Electron and ion trajectory calculations are presented, and the performance illustrated with six molecules having attachment resonances in the range 0.0–2.2 eV. The detection sensitivity as measured using the method of standard additions is below 1 part-per-trillion, with a calculated conversion rate (ions/electrons) of 1.3%. Signal nonlinearity is discussed in terms of ion space-charge effects. The device also produces positive ions, and an analogous treatment may be carried through to characterize its performance in this mode.

Increased response of the reversal electron attachment detector and modelling of ion space-charge effects

Design and sensitivity tests of a modified version of the so-called reversal electron attachment detector (READ) are presented. The new version uses a spherical cathode capable of emitting higher electron currents. As in the original READ (which used a planar emitter) electrons are focused into an electrostatic mirror which reverses their trajectories. In the reversal region electrons have essentially zero energy and attach to target molecules to form negative ions. The electron gun lens system has been modified using a field and trajectory code with space charge included. Electron trajectories have been calculated for 1-mA current focused into a reversal region of 3.5-mm diameter. The detection limit of the apparatus is approximately 25 times lower than for the original READ. Nonlinearity in the measured signal vs electron current is described by a model in which a spherical ball of ions expands outward with velocity determined by the space-charge force and the initial velocity of ion formation.

Cesium ion desorption from oxygen and carbon adlayers on platinum surfaces with nanosecond time resolution: Variation of desorption parameters with time available for surface diffusion and degree of surface heterogeneity

Measurements of ionic cesium desorption from surfaces at temperatures above 1100 K have been made with the so-called field reversal method. Time constants down to 30 ns have been measured with very low surface densities of Cs. The prexponential factors for desorption from clean platinum and graphite covered platinum surfaces are close to 10 12 s −1, in agreement with simple desorption theory. However, for slightly oxygen covered surfaces and for carbon layers formed at low temperatures the preexponential and the desorption energy become significantly larger, while a strict Arrhenius form is retained. This is proposed to be due to the influence of surface inhomogeneity and surface diffusion, in line with the theoretical description of simultaneous diffusion and desorption recently given by Nordholm. In the oxygen case, the adsorbed oxygen is considered to be the origin of the heterogeneity, while in the carbon layer case the surface, which has been formed at low temperature, is disordered and may contain many strongly binding sites. The influence of bulk diffusion on the desorption is also described.

Operation and mass resolution of a time-of-flight mass spectrometer with electron impact ionization and rapid field reversal

An analysis of the function of a novel time-of-flight mass spectrometer with rapid field switching on one grid, the so-called field reversal grid, is given. The field switching is non-conservative, such that the ions enter the flight region at ground potential with an energy higher than the total energy at their formation. The pulsing and acceleration are both made with one grid. An ion mirror reduces the spread in flight times due to the initial ion energy. The mass spectrometer source can be operated in two different modes. In the most efficient and most easily analyzed mode there is no ion turn-around problem, since the ions are not accelerated out through the field reversal grid. Instead, they drift out during deceleration and are then repelled away from the grid. An expression for the mass resolution has been derived, which is in good agreement with experimental results from the mass spectrometer described in a companion article.

Imponderables of the Holocaust

Recent literature, particularly in Germany and the Netherlands, has provided insights into some of the most perplexing imponderables of the Nazi annihilation of the Jews. These are, first, the development of consensus among the various German elites for the purposes of the Final Solution; second, an incremental kind of German decision making which led to the efficiently implemented mass annihilation of the Jews; and third, the passive mood toward the disasters befalling the Jews on the part of the entire universe of bystanders. (In the case of the Netherlands, this resulted, in spite of an unusually low degree of anti-Semitism, in an unusually high degree of Jewish victimization—in contrast to the so-called Danish reversal.) Fourth, because of the unimaginable predicament experienced by the victims and their “governments,” the Jewish Councils (such as the AmsterdamJoodsche Raad), they never had a chance to develop workable responses to such a catastrophe.

A Method for Quantity Developing of Motion Picture Films*

This paper describes an improved machine for developing motion picture negative films in use at the laboratories of the Universal Pictures Corp. A thorough description of the machine and its operation is given. The system involves the so-called reversal process.

ARTERIOVENOUS ANASTOMOSIS

Early in 1913 I 1 reported a case wherein an arteriovenous anastomosis—so-called reversal of the circulation—had been done in all four extremities for the relief of real and threatened gangrene consequent on Raynaud's disease. This was in the days when the Carrel method of suturing blood vessels had become available to clinical uses and when so much was expected of it. The case was that of a young woman under the care of Dr. Joseph C. Bloodgood, who not only assisted at one of the operations but graciously consented to the report after all the work had been completed. Dr. Bloodgood has the patient in his wards at the St. Agnes Hospital once again and has kindly permitted me to study her and make the present follow-up report. In brief, the woman, Mrs. G., was 26 years of age when in February, 1911, an arteriovenous anastomosis of the femoral artery