6,552 research outputs found
Tetragonal to triclinic structural transition in the prototypical CeScSi induced by a two-step magnetic ordering: a temperature-dependent neutron diffraction study of CeScSi, CeScGe and LaScSi
No full textAn investigation on the ground state magnetism of CeScSi, CeScGe (tetragonal CeScSi-type, tI12, space group I4/mmm) by temperature-dependent powder neutron diffraction has been carried out, as debated and controversial data regarding the low temperature magnetic behaviours of these two compounds were reported. Our studies reveal that, while cooling, long-range magnetic ordering in CeScSi and CeScGe takes place by a two-step process. A first transition leads to a magnetic structure with the Ce moments aligned ferromagnetically onto two neighbouring tetragonal basal a-b planes of the CeScSi-type structure; the double layers are then antiferromagnetically coupled to each other along the c-axis. The transition temperature associated with the first ordering is T N ~ 26 K and T N ~ 48 K for the silicide and the germanide, respectively. Here the spin directions are rigorously confined to the basal plane, with values of the Ce magnetic moments of μ Ce = 0.8-1.0 μ B. A second magnetic transition, which takes place at slightly lower temperatures, results in a canting of the ordered magnetic moments out of the basal plane which is accompanied by an increase of the magnetic moment value of Ce to μ Ce = 1.4-1.5 μ B. Interestingly, the second magnetic transition leads to a structural distortion in both compounds from the higher-symmetry tetragonal space group I4/mmm to the lower-symmetry and triclinic I-1 (non-standard triclinic). Magnetic symmetry analysis shows that the canted structure would not be allowed in the I4/mmm space group; this result further confirms the structural transition. The transition temperatures T S from I4/mmm to I-1 are about 22 K in CeScSi and 36 K in CeScGe, i.e. well below the temperature of the first onset of antiferromagnetic order observed in this work (or below the ordering temperature, previously reported as either T C or T N). This result, along with the synchronism of the magnetic and structural transitions, suggests a magnetostructural origin of this structural distortion. We have also carried out powder neutron diffraction for LaScSi as a non-magnetically-ordering reference compound and compared the results with those of CeScSi and CeScGe compounds
Magnetic ground states of Ce3TiSb5, Pr3TiSb5and Nd3TiSb5 determined by neutron powder diffraction and magnetic measurements
No full textThe R 3TiSb5 ternary compounds, with R a light rare earth (La to Sm) have been reported to crystallize with the anti-Hf5CuSn3-type hexagonal structure (Pearson's symbol hP18; space-group P63/mcm, N. 193). An early article that reported possible superconductivity in some of these intermetallic phases (namely those with R = La, Ce, and Nd) caught our attention. In this work, we have now refined the crystal structure of the R 3TiSb5 compounds with R = Ce, Pr and Nd by Rietveld methods using high-resolution neutron powder diffraction data. The magnetic ground states of these intermetallics have been investigated by low-temperature magnetization and high-intensity neutron diffraction. We find two different magnetic transitions corresponding to two related magnetic structures at T N1 = 4.8 K (k 1 = [0, 1/2, 1/8]) and T N2 = 3.4 K (k 2 = [0, 0, 1/8]), respectively for Ce3TiSb5. However, the magnetic ordering appears to occur following a peculiar hysteresis: the k 2-type magnetic structure develops only after the k 1-type phase fraction has first slowly ordered with time and the size of the ordered Ce3+ magnetic moment has become large enough to induce the second magnetic transition. At T = 1.5 K the maximum amplitude of the Ce moment in the coexisting phases amounts to μ Ce = 2.15 μ B. For Nd3TiSb5 an antiferromagnetic ordering below T N = 5.2 K into a relatively simpler commensurate magnetic structure with a magnetic moment of μ Nd = 2.14(3) μ B and magnetic propagation vector of k = [0, 0, 0], was determined. No evidence of superconductivity has been found in Nd3TiSb5. Finally, Pr3TiSb5 does not show any ordering down to 1.5 K in neutron diffraction while an antiferromagnetic ground state is detected in magnetization measurements. There is no sign of magnetic contribution from Ti atoms found in any of the studied compounds
Formation, Stability and Magnetism of New Gd3TAl3Ge2 Quaternary Compounds (T = Mn, Cu)
No full textA study on the formation and stability of new quaternary compounds with the general chemical formula Gd3TAl3Ge2 (T = Mn, Cu) has been undertaken by experimental investigations (SEM-EDX, DTA and XRD) and density functional theory (DFT) calculations. These compounds crystallize in the hexagonal Y3NiAl3Ge2-type structure (hP9, P–62m, Z = 1) (an ordered, quaternary derivative of the ternary ZrNiAl or of the binary Fe2P prototypes), with lattice parameters values a = 7.0239(2) Å and c = 4.2580(1) Å for Gd3MnAl3Ge2 and a = 7.0434(1) Å and c = 4.2089(1) Å for Gd3CuAl3Ge2. DTA suggests a peritectic reaction for the formation of these compounds (at 1245 degrees C for Gd3CuAl3Ge2). The existence and stability of these phases has been explained on the basis of DFT calculations, and a comparison of ground state properties of the studied compounds with the earlier known Gd3CoAl3Ge2 phase is outlined. The negative formation energies in all three cases govern the stability of compounds from theory as well, predicting Gd3MnAl3Ge2 as the most stable phase with highest formation energy (–13.01 eV/f.u.). The total DOS are generic in nature and suggest the robust magnetism, with the Gd-f moments of approximately equal to 7 the Bohr magnetons. An antiparallel coupling among Gd-f and T-d states is observed for all compounds, as usually seen in rare earth (R) - transition metal (T) compounds. Preliminary magnetization measurements on Gd3MnAl3Ge2 show two ferromagnetic/ferrimagnetic (FM/FIM) like transitions at TC1 = 142 K and TC2 = 97 K, with another anomaly seen at approximately equal to15 K. Isothermal magnetization data show no hysteresis even at 5 K, and the magnetization does not saturate up to 50 kOe, further suggesting a possible FIM behavior.</p
Fixed and coincidence points of hybrid mappings
No full textsummary:The purpose of this note is to provide a substantial improvement and appreciable generalizations of recent results of Beg and Azam; Pathak, Kang and Cho; Shiau, Tan and Wong; Singh and Mishra
Radial distribution functions of water: Models vs experiments
No full textWe study the temperature behavior of the first four peaks of the oxygen-oxygen radial distribution function of water, simulated by the TIP4P/2005, MB-pol, TIP5P, and SPC/E models and compare to experimental X-ray diffraction data, including a new measurement which extends down to 235 K [H. Pathak et al., J. Chem. Phys. 150, 224506 (2019)]. We find the overall best agreement using the MB-pol and TIP4P/2005 models. We observe, upon cooling, a minimum in the position of the second shell simulated with TIP4P/2005 and SPC/E potentials, located close to the temperature of maximum density. We also calculated the two-body entropy and the contributions coming from the first, second, and outer shells to this quantity. We show that, even if the main contribution comes from the first shell, the contribution of the second shell can become important at low temperature. While real water appears to be less ordered at short distance than obtained by any of the potentials, the different water potentials show more or less order compared to the experiments depending on the considered length-scale
Magnetic and transport behaviors of non-centrosymmetric Nd7Ni2Pd
No full textCrystallographic, magnetic, electrical transport and thermodynamic properties of pseudo-binary Nd7Ni2Pd compound have been studied using temperature-dependent x-ray powder diffraction and physical property measurements. Compared to the ferromagnetic parent Nd7Pd3, the ground state of Nd7Ni2Pd is antiferromagnetic, and it exhibits strong metamagnetism. The measurements indicate two antiferromagnetic transitions in fields less than 8 kOe: a second-order paramagnetic to antiferromagnetic at TN2 = 29 K and a weak first-order antiferromagnetic to antiferromagnetic transition at TN1 = 24.5 K. The compound becomes ferromagnetic in fields of 8 kOe and higher with TC = 30 K. Temperature dependence of lattice parameters is anomalous, most prominently in the basal plane at ∼30 K; however, there is no detectable structural distortion or clear volume discontinuity around 25 K, suggesting a significant weakening of the first-order transition when compared to the binary Nd7Pd3.</p
Sleep apnea and cardiac arrhythmia: a timely wake-up call!
No full textRajeev K. Pathak, Rajiv Mahajan, Dennis H. Lau, Prashanthan Sander
A Compilation Framework for Macroprogramming Networked Sensors
No full textAbstract. Macroprogramming—the technique of specifying the behavior of the system, as opposed to the constituent nodes—provides application developers with high level abstractions that alleviate the programming burden in develop- ing wireless sensor network (WSN) applications. However, as the semantic gap between macroprogramming abstractions and node-level code is considerably wider than in traditional programming, converting the high level specification to running code is a daunting process, and a major hurdle to the acceptance of macroprogramming.
In this paper, we propose a general compilation framework for a data-driven macroprogramming language that allows for plugging in different modules implementing various stages of compilation. We also demonstrate an actual instantiation of our framework by showing an end-to-end solution for compiling macro- programs. Our compiler provides the final code to be deployed on real nodes as well as an estimate of the costs the running system will incur, e.g., in terms of messages exchanged. We compared the auto-generated code against a hand- coded version for the same application behavior to verify the outcome of our compiler
Recent progress in electrochromic energy storage materials and devices: a minireview
No full textIntegration of several functionalities into one isolated electrochemical body is necessary to realize compact and tiny smart electronics. Recently, two different technologies, electrochromic (EC) materials and energy storage, were combined to create a single system that supports and drives both functions simultaneously. In EC energy storage devices, the characteristic feature of EC materials, their optical modulation depending on the applied voltage, is used to visually identify the stored energy level in real time. Moreover, combining energy-harvesting and EC storage systems by sharing one electrode facilitates the realization of further compact multifunction systems. In this minireview, we highlight recent groundbreaking achievements in EC multifunction systems where the stored energy levels can be visualized using the color of the device.
Enzyme-free, metal oxide-based amperometric-colorimetric dual-mode functional glucose sensor
No full textTo address the urgent need for glucose level detection in the human body, several affordable, lightweight, and skin-mounted glucose sensors have been developed. Enzymatic sensors are frequently utilized, but they have challenges of enzyme degradation and indirect charge transfer through a redox mediator, which affect their reusability and shelf life. Here, enzyme-free nickel oxide thin film electrode in an alkaline medium is used to enable direct charge transfer with glucose. A chemical reaction between glucose and the electrode surface occurs, leading to an additional oxidation (Ni+2/Ni+3) of the electrode under external bias. Additionally, the colorimetric analysis further validated this reaction through the transformation of a dark-colored NiO (Ni+3) electrode into a bleached color state (reduced from Ni+3 to Ni+2) through the oxidation of glucose. As the glucose concentrations increase to 5 mM, the color of the electrode is no longer optically readable (Delta T% similar to 66%). The corresponding amperometric response is determined with a detection limit of 2 mu M and a 3579 mu A mM(-1) cm(-2) sensitivity, and it also recognizes a passive response to other interfering species and facilitates its one-month shelf life. Additionally, a two-electrode electrochemical colorimetric liquid cell-type glucose sensor has been designed to pave the way for future applications.
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