Investigations of the effect of nonmagnetic Ca substitution for magnetic Dy on spin-freezing in Dy2Ti2O7

Physical properties of partially Ca substituted hole-doped Dy2Ti2O7 have been investigated by ac magnetic susceptibility \chi_ac(T), dc magnetic susceptibility \chi(T), isothermal magnetization M(H) and heat capacity C_p(T) measurements on Dy1.8Ca0.2Ti2O7. The spin-ice system Dy2Ti2O7 exhibits a spin-glass type freezing behavior near 16 K. Our frequency dependent \chi_ac(T) data of Dy1.8Ca0.2Ti2O7 show that the spin-freezing behavior is significantly influenced by Ca substitution. The effect of partial nonmagnetic Ca2+ substitution for magnetic Dy3+ is similar to the previous study on nonmagnetic isovalent Y3+ substituted Dy2-xYxTi2O7 (for low levels of dilution), however the suppression of spin-freezing behavior is substantially stronger for Ca than Y. The Cole-Cole plot analysis reveals semicircular character and a single relaxation mode in Dy1.8Ca0.2Ti2O7 as for Dy2Ti2O7. No noticeable change in the insulating behavior of Dy2Ti2O7 results from the holes produced by 10% Ca2+ substitution for Dy3+ ions.Comment: 9 pages, 7 figures, 1 tabl

Integrating Nanosphere Lithography in Device Fabrication

This paper discusses the integration of nanosphere lithography (NSL) with other fabrication techniques, allowing for nano-scaled features to be realized within larger microelectromechanical system (MEMS) based devices. Nanosphere self-patterning methods have been researched for over three decades, but typically not for use as a lithography process. Only recently has progress been made towards integrating many of the best practices from these publications and determining a process that yields large areas of coverage, with repeatability and enabled a process for precise placement of nanospheres relative to other features. Discussed are two of the more common self-patterning methods used in NSL (i.e. spin-coating and dip coating) as well as a more recently conceived variation of dip coating. Recent work has suggested the repeatability of any method depends on a number of variables, so to better understand how these variables affect the process a series of test vessels were developed and fabricated. Commercially available 3-D printing technology was used to incrementally alter the test vessels allowing for each variable to be investigated individually. With these deposition vessels, NSL can now be used in conjunction with other fabrication steps to integrate features otherwise unattainable through current methods, within the overall fabrication process of larger MEMS devices. Patterned regions in 1800 series photoresist with a thickness of ~700nm are used to capture regions of self-assembled nanospheres. These regions are roughly 2-5 microns in width, and are able to control the placement of 500nm polystyrene spheres by controlling where monolayer self-assembly occurs. The resulting combination of photoresist and nanospheres can then be used with traditional deposition or etch methods to utilize these fine scale features in the overall design

Gravitational Collapse of Dust with a Cosmological Constant

The recent analysis of Markovic and Shapiro on the effect of a cosmological constant on the evolution of a spherically symmetric homogeneous dust ball is extended to include the inhomogeneous and degenerate cases. The histories are shown by way of effective potential and Penrose-Carter diagrams.Comment: 2 pages, 2 figures (png), revtex. To appear in Phys. Rev.

Engineered surfaces to control secondary electron emission for multipactor suppression

A significant problem for space-based systems is multipactor - an avalanche of electrons caused by repeated secondary electron emission (SEE). The consequences of multipactor range from altering the operation of radio frequency (RF) devices to permanent device damage. Existing efforts to suppress multipactor rely heavily on limiting power levels below a multipactor threshold [1]. This research applies surface micromachining techniques to create porous surfaces to control the secondary electron yield (SEY) of a material for multipactor suppression. Surface characteristics of interest include pore aspect ratio and density. A discussion is provided on the advantage of using electroplating (vice etching) to create porous surfaces for studying the relationships between SEY and pore aspect ratio & density (i.e. porosity). Preventing multipactor through SEY reduction will allow power level restrictions to be eased, leading to more powerful and capable space-based systems

Observation of long range magnetic ordering in pyrohafnate Nd2Hf2O7: A neutron diffraction study

We have investigated the physical properties of a pyrochlore hafnate Nd2Hf2O7 using ac magnetic susceptibility \chi_ac(T), dc magnetic susceptibility \chi(T), isothermal magnetization M(H) and heat capacity C_p(T) measurements, and determined the magnetic ground state by neutron powder diffraction study. An upturn is observed below 6 K in C_p(T)/T, however both C_p(T) and \chi(T) do not show any clear anomaly down to 2 K. The \chi_ac(T) shows a well pronounced anomaly indicating an antiferromagnetic transition at T_N = 0.55 K. The long range antiferromagnetic ordering is confirmed by neutron diffraction. The refinement of neutron diffraction pattern reveals an all-in/all-out antiferromagnetic structure, where for successive tetrahedra, the four Nd3+ magnetic moments point alternatively all-into or all-out-of the tetrahedron, with an ordering wavevector k = (0, 0, 0) and an ordered state magnetic moment of m = 0.62(1) \mu_B/Nd at 0.1 K. The ordered moment is strongly reduced reflecting strong quantum fluctuations in ordered state.Comment: 10 pages, 9 figures and 2 tables; to appear in Phys. Rev.

Junctions and thin shells in general relativity using computer algebra I: The Darmois-Israel Formalism

We present the GRjunction package which allows boundary surfaces and thin-shells in general relativity to be studied with a computer algebra system. Implementing the Darmois-Israel thin shell formalism requires a careful selection of definitions and algorithms to ensure that results are generated in a straight-forward way. We have used the package to correctly reproduce a wide variety of examples from the literature. We present several of these verifications as a means of demonstrating the packages capabilities. We then use GRjunction to perform a new calculation - joining two Kerr solutions with differing masses and angular momenta along a thin shell in the slow rotation limit.Comment: Minor LaTeX error corrected. GRjunction for GRTensorII is available from http://astro.queensu.ca/~grtensor/GRjunction.htm

Investigation of the magnetic structure and crystal field states of pyrochlore antiferromagnet Nd2Zr2O7

We present synchrotron x-ray diffraction, neutron powder diffraction and time-of-flight inelastic neutron scattering measurements on the rare earth pyrochlore oxide Nd2Zr2O7 to study the ordered state magnetic structure and cystal field states. The structural characterization by high-resolution synchrotron x-ray diffraction confirms that the pyrochlore structure has no detectable O vacancies or Nd/Zr site mixing. The neutron diffraction reveals long range all-in/all-out antiferromagnetic order below T_N ~ 0.4 K with propagation vector k = (0 0 0) and an ordered moment of 1.26(2) \mu_B/Nd at 0.1 K. The ordered moment is much smaller than the estimated moment of 2.65 \mu_B/Nd for the local Ising ground state of Nd3+ (J=9/2) suggesting that the ordering is partially suppressed by quantum fluctuations. The strong Ising anisotropy is further confirmed by the inelastic neutron scattering data which reveals a well-isolated dipolar-octupolar type Kramers doublet ground state. The crystal field level scheme and ground state wavefunction have been determined.Comment: 12 pages, 15 figures, 2 table

Real-Time Maps of Fluid Flow Fields in Porous Biomaterials

Mechanical forces such as fluid shear have been shown to enhance cell growth and differentiation, but knowledge of their mechanistic effect on cells is limited because the local flow patterns and associated metrics are not precisely known. Here we present real-time, noninvasive measures of local hydrodynamics in 3D biomaterials based on nuclear magnetic resonance. Microflow maps were further used to derive pressure, shear and fluid permeability fields. Finally, remodeling of collagen gels in response to precise fluid flow parameters was correlated with structural changes. It is anticipated that accurate flow maps within 3D matrices will be a critical step towards understanding cell behavior in response to controlled flow dynamics.Comment: 23 pages, 4 figure

Pengaruh Subtitusi Ampas Tahu pada Pakan BR2 terhadap Berat Hidup, Berat Potong, Berat Dada dan Berat Paha Ayam Broiler

This study aims to determine the effect of tofu dregs substitution in BR2 feed on live weight, cut weight, breast weight and thigh weight for broiler chickens. This research was carried out in Poultry Housing of Animal Husbandry Study Program and the Laboratory of Agriculture Faculty, Timor University during 48 days, from July until August, 2020. This research used 96 broilers that is days old chick. The experimental design used the completely randomized design (CRD) consist of four treatments and four replication. The treatment that given is: P0 (100% commercial BR2 feed), P1 (95% commercial BR2 feed + tofu waste 5%), P2 (90% commercial BR2 feed + tofu waste 10%), and P3 (85% commercial BR2 feed + tofu waste 15%). The observed variables are live weight, cut weight, percentage of cut weight, breast weight, percentage of breast weight, thigh weight and percentage of thigh weight. The results of statistical analysis show that substitution of tofu waste in BR2 feed from a level of 0.05% to a level 0,10% can increase breast weight, but had no effect on live weight, cut weight and thigh weight of broiler chickens. It was eliminated that tofu pulp can be used to replace BR2 feed by 10%.Penelitian ini bertujuan mengetahui pengaruh subtitusi ampas tahu pada pakan BR2 terhadap berat hidup, berat potong, berat dada dan berat paha ayam broiler. Penelitian ini dilaksanakan di Kandang Ternak Unggas Program Studi Peternakan dan Laboratorium Fakultas Pertanian Universitas Timor, Kefamenanu selama 42 hari, sejak bulan Juli sampai Agustus 2020. Penelitian ini menggunakan 96 ekor ayam broiler umur sehari (Day Old Chick). Rancangan percobaan yang digunakan adalah Rancangan Acak Lengkap (RAL) pola searah, terdiri dari 4 perlakuan dan 4 ulangan. Perlakuan yang diberikan adalah P0(100% pakan BR2 komersial), P1(95% pakan BR2 komersial + ampas tahu 5%), P2(90% pakan BR2 komersial + ampas tahu 10%) dan P3 (85% pakan BR2 komersial + ampas tahu 15%). Variabel yang diamati adalah berat hidup, berat potong, persentase berat potong, berat dada, persentase berat dada, berat paha dan persentase berat paha. Analisis statistik menunjukkan bahwa subtitusi ampas tahu dalam pakan BR2 dari level 0,5% sampai dengan level 15 % berpengaruh tidak nyata terhadap berat hidup, berat potong, berat dada dan berat paha ayam broiler. Disimpulkan bahwa ampas tahu dapat digunakan untuk menggantikan pakan BR2 sebesar 15%