Fermi acceleration and suppression of Fermi acceleration in a time-dependent Lorentz Gas

We study some dynamical properties of a Lorentz gas. We have considered both the static and time dependent boundary. For the static case we have shown that the system has a chaotic component characterized with a positive Lyapunov Exponent. For the time-dependent perturbation we describe the model using a four-dimensional nonlinear map. The behaviour of the average velocity is considered in two situations (i) non-dissipative and (ii) dissipative. Our results show that the unlimited energy growth is observed for the non-dissipative case. However, when dissipation, via damping coefficients, is introduced the senary changes and the unlimited engergy growth is suppressed. The behaviour of the average velocity is described using scaling approach

Shuttle Test and Operations Approach

The Shuttle Program presently under development is one which challenges our ingenuity. In its infancy we see that old and tried test techniques and approaches may no longer be valid and that in order to meet program goals of minimum cost and high reliability, new test and operation plans and methods must be conceived. This paper presents an over view of the Space Shuttle Test and Operations Program. I will briefly touch on today\u27s test/ operations requirements, the concept under which they have been developed and their implementation. Several of the concepts presented are a direct result of our Phase B Shuttle Study and are presently under program consideration. The Space Shuttle Program embodies design, production, test, operations and support attributes and/ or problems of both the aircraft and the missile. The operational concept is particularly unique in that a small number of recoverable flight vehicles operating in both the vertical and horizontal flight modes will be deployed to or from one primary operation site. For these and other reasons, the Shuttle Program presents unusual opportunities for development and implementation of an efficient and cost effective ground and flight test approach based on sound test and operational criteria

Antiferromagnetic spin chain behavior and a transition to 3D magnetic order in Cu(D,L-alanine)2: Roles of H-bonds

We study the spin chain behavior, a transition to 3D magnetic order and the magnitudes of the exchange interactions for the metal-amino acid complex Cu(D,L-alanine)2.H2O, a model compound to investigate exchange couplings supported by chemical paths characteristic of biomolecules. Thermal and magnetic data were obtained as a function of temperature (T) and magnetic field (B0). The magnetic contribution to the specific heat, measured between 0.48 and 30 K, displays above 1.8 K a 1D spin-chain behavior that can be fitted with an intrachain antiferromagnetic (AFM) exchange coupling constant 2J0 = (-2.12 $\pm$ 0.08) cm$^{-1}$, between neighbor coppers at 4.49 {\AA} along chains connected by non-covalent and H-bonds. We also observe a narrow specific heat peak at 0.89 K indicating a phase transition to a 3D magnetically ordered phase. Magnetization curves at fixed T = 2, 4 and 7 K with B0 between 0 and 9 T, and at T between 2 and 300 K with several fixed values of B0 were globally fitted by an intrachain AFM exchange coupling constant 2J0 = (-2.27 $\pm$ 0.02) cm$^{-1}$ and g = 2.091 $\pm$ 0.005. Interchain interactions J1 between coppers in neighbor chains connected through long chemical paths with total length of 9.51 {\AA} are estimated within the range 0.1 < |2J1| < 0.4 cm$^{-1}$, covering the predictions of various approximations. We analyze the magnitudes of 2J0 and 2J1 in terms of the structure of the corresponding chemical paths. The main contribution in supporting the intrachain interaction is assigned to H-bonds while the interchain interactions are supported by paths containing H-bonds and carboxylate bridges, with the role of the H-bonds being predominant. We compare the obtained intrachain coupling with studies of compounds showing similar behavior and discuss the validity of the approximations allowing to calculate the interchain interactions.Comment: 10 pages, 4 figure

The Goss Lemming Mouse, \u3ci\u3eSynaptomys cooperi gossii\u3c/i\u3e (Goues), in Nebraska

In the course of studies on the cestode parasites of microtine rodents by one of the authors (Hansen), specimens of mice were sent to the United State National Museum where they were identified by Dr. David H. Johnson. Two of these microtines proved to be Synaptomys cooperi gossii (Coues). These specimens of Synaptomys (U.S.N.M. Nos. 282343 and 282344), collected at Lincoln, Lancaster County, Nebraska, on September 16, 1946 (male) and November 20, 1946 (female), respectively, are the first ones to be identified from Nebraska

Consequences of Quadratic Frictional Force on the One Dimensional Bouncing Ball Model

Some dynamical properties of the one dimensional Fermi accelerator model, under the presence of frictional force are studied. The frictional force is assumed as being proportional to the square particle's velocity. The problem is described by use of a two dimensional non linear mapping, therefore obtained via the solution of differential equations. We confirm that the model experiences contraction of the phase space area and in special, we characterized the behavior of the particle approaching an attracting fixed point. © 2007 American Institute of Physics

Exchange-spring behavior in bimagnetic CoFe2O4/CoFe2 nanocomposite

In this work we report a study of the magnetic behavior of ferrimagnetic oxide CoFe2O4 and ferrimagnetic oxide/ferromagnetic metal CoFe2O4/CoFe2 nanocomposites. The latter compound is a good system to study hard ferrimagnet/soft ferromagnet exchange coupling. Two steps were used to synthesize the bimagnetic CoFe2O4/CoFe2 nanocomposites: (i) first preparation of CoFe2O4 nanoparticles using the a simple hydrothermal method and (ii) second reduction reaction of cobalt ferrite nanoparticles using activated charcoal in inert atmosphere and high temperature. The phase structures, particle sizes, morphology, and magnetic properties of CoFe2O4 nanoparticles have been investigated by X-Ray diffraction (XRD), Mossbauer spectroscopy (MS), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM) with applied field up to 3.0 kOe at room temperature and 50K. The mean diameter of CoFe2O4 particles is about 16 nm. Mossbauer spectra reveal two sites for Fe3+. One site is related to Fe in an octahedral coordination and the other one to the Fe3+ in a tetrahedral coordination, as expected for a spinel crystal structure of CoFe2O4. TEM measurements of nanocomposite show the formation of a thin shell of CoFe2 on the cobalt ferrite and indicate that the nanoparticles increase to about 100 nm. The magnetization of nanocomposite showed hysteresis loop that is characteristic of the exchange spring systems. A maximum energy product (BH)max of 1.22 MGOe was achieved at room temperature for CoFe2O4/CoFe2 nanocomposites, which is about 115% higher than the value obtained for CoFe2O4 precursor. The exchange-spring interaction and the enhancement of product (BH)max in nanocomposite CoFe2O4/CoFe2 have been discussed.Comment: 9 pages, 10 figure

Opportunistic Infections and Associated Factors among HIV Infected Patients on Anti-Retroviral Treatment at Bombo Hospital in Tanga Region, Tanzania

Background: A substantive number of People Living with HIV (PLHIV) develop Opportunistic Infections (OIs). The introduction of Anti-Retroviral Therapy (ART) in Tanzania led to a significant decline in opportunistic infections and a slower progression to AIDS, but OIs are still prevalent. This study was set to determine the magnitude of OIs and associated factors among HIV/AIDS patients on Anti-Retroviral Therapy (ART) attending care and treatment clinic at Bombo Regional Referral hospital, Tanga region. Materials and Methods: A cross‐sectional descriptive study was conducted on HIV/AIDS patients on ART attending Bombo Hospital in Tanga from July to October 2019. A non-probability, consecutive sampling technique was employed to obtain study participants. Data were collected using available data obtained from the patients’ files, hospital record books and interviews of study participants by using semi-structured questionnaires. Data were entered into the computer using Excel 2013, cleaned and analysed using Epi Info version 7.2.2.6. Any p-value of &lt; 0.05, at a 95% confidence interval was regarded as statistically significant. Results: The study showed that out of the 360 participants, 126 cases (35.0%) of OIs were reported. Pulmonary Tuberculosis had the highest prevalence of 18.0% among PLHIV while other opportunistic Infections altogether contributed 17.0%. Late ART initiation (OR=10.9, 95% CI: 6.5 – 18.3, p-value &lt;0.001), Poor drug adherence (OR=19, 95% CI: 9.0 – 39.7, p-value &lt;0.001), female gender (69% vs. 31%), which was however, not statistically significant (p-value – 0.904), Informal and Primary School education (OR = 1.6, 95% CI: 1.1 – 1.6, p-value 0.04) being married (OR=2.1, 95% CI: 1.3 – 3.4, p – value 0.004) and widowed/widower (OR=7.7, 95% CI: 1.7 – 33.7, p – value 0.007) respectively were found to be associated with OIs to PLHIV. Conclusion: The rate of OIs still high among PLHIV, Pulmonary Tuberculosis is the leading disease with 18.0% of all OIs symptomatic patients. Delay in ART initiation after positive test results, poor drug adherence and moderate malnutrition have been identified as major risk factors affecting 66.0%, 70.0%, 71%of PLWHA with OIs. We recommend early initiation of ART, Education on ART adherence and refilling of large quantities of ARV drugs to individuals working far from their homes