Sources of Real Exchange Rate Fluctuations: How Important Are Nominal Shocks?

This paper investigates empirically and attempts to identify the sources of real exchange rate fluctuations since the collapse of Bretton Woods. The paper's first two sections survey and extend earlier, non-structural empirical work on this subject by Campbell and Clarida (1987), Meese and Rogoff (1988), and Cumby and Huizinga (1990). The paper's main contribution is to build and estimate a three equation open macro model in the spirit of Dornbusch (1976) and Obstfeld (1985) and to identify the model's structural shocks to demand, supply, and money - using the approach pioneered by Blanchard and Quah (1989). For two of the four countries we study, Germany and Japan, our structural estimates imply that monetary shocks, to money supply as well as to the demand for real money balances, explain a substantial amount of the variance of real exchange rates relative to the dollar. We find that demand shocks, to national saving and investment, explain the majority of the variance in real exchange rate fluctuations, while supply shocks explain very little. The model's estimated short run dynamics are strikingly consistent with the predictions of the simple textbook Mundell-Fleming model

Characterization of the nitrogen split interstitial defect in wurtzite aluminum nitride using density functional theory

We carried out Heyd-Scuseria-Ernzerhof hybrid density functional theory plane wave supercell calculations in wurtzite aluminum nitride in order to characterize the geometry, formation energies, transition levels and hyperfine tensors of the nitrogen split interstitial defect. The calculated hyperfine tensors may provide useful fingerprint of this defect for electron paramagnetic resonance measurement.Comment: 5 pages, 3 figure

Modelling the transfer function of two-dimensional SQUID and SQIF arrays with thermal noise

We present a theoretical model for 2D SQUID and SQIF arrays with over-damped Josephson junctions for uniform bias current injection at 77 K. Our simulations demonstrate the importance of including Johnson thermal noise and reveal that the mutual inductive coupling between SQUID loops is of minor importance. Our numerical results establish the validity of a simple scaling behaviour between the voltages of 1D and 2D SQUID arrays and show that the same scaling behaviour applies to the maximum transfer functions. The maximum transfer function of a 2D SQUID array can be further optimised by applying the optimal bias current which depends on the SQUID loop self-inductance and the junction critical current. Our investigation further reveals that a scaling behaviour exits between the maximum transfer function of a 2D SQUID array and that of a single dc-SQUID. Finally, we investigate the voltage response of 1D and 2D SQIF arrays and illustrate the effects of adding spreads in the heights and widths of SQUID loops.Comment: 9 Figures Submitted to PR

The effect of bias current configuration on the performance of SQUID arrays

Designing superconducting electronic devices involves a careful study of all the elements in the circuit, including the superconducting bias leads, however, the effect of the bias current leads on the performance of the device have not been previously addressed. In this work, we introduce a theoretical model for two-dimensional superconducting quantum interference device (SQUID) arrays capable of simulating the response of devices with different bias current configurations. First, we compare uniformly biased and centre biased SQUID arrays by investigating the voltage versus magnetic flux response, maximum transfer function and voltage modulation depth. Then, we calculate the time-averaged fluxoid distributions for 1D and 2D centre biased arrays. Finally, we study the performance of the two bias current configurations depending on array size, screening parameter, thermal noise strength and kinetic self-inductance fraction. Our calculations reveal: (i) centre biased 1D parallel SQUID arrays present an unusual voltage response caused by the asymmetric fluxoid distribution; (ii) the optimal transfer function of centre biased arrays strongly depends on the number of junctions in parallel; (iii) the performance of centre biased arrays approaches the uniform biased ones when the number of junctions in series exceeds those in parallel; (iv) while the screening parameter and the thermal noise strength clearly affect the device performance, the kinetic self-inductance fraction seems to play only a secondary role.Comment: 10 pages, 9 Figure

Assessment of serum total protein, albumin and calcium in pregnant women attending ante-natal clinic, University of Maiduguri Teaching Hospital

Background: Pregnancy is a normal physiological phenomenon with many biochemical changes including calcium metabolism. Calcium requirement increases during pregnancy, thereby increasing the chances of developing hypocalcaemia and hypoalbuminaemia. Aim: The aim of the present study was to assess serum levels of total protein, albumin, and calcium among pregnant women in University of Maiduguri Teaching Hospital Maiduguri, Borno State. Methodology: A total of two hundred (200) subjects were recruited for this study. One hundred and twenty (120) are confirmed pregnant women and 80 non pregnant women age matched were used as controls, out of the 120 pregnant women that participated in the study, 30 were in first trimester, 50 were in second trimester and 40 were in third trimester. Blood chemistry analysis was conducted spectrophotometrically using Biurets method (For Total protein), Bromocresol green method (for Albumin) and O-Cresolphthalein complex one (for calcium). Results: The results show a significant lower value of calcium and albumin (p<0.05) among first trimester pregnant women when compared to the control subjects. The results show a significant decrease in calcium and albumin (p<0.05) among second trimester pregnant women when compared to control subjects. The results show a significant lower value in calcium and albumin (p<0.05) among third trimester pregnant women when compared to control subjects. The results between 1st, 2nd and 3rd trimester pregnant women subjects show a significant difference in calcium and albumin (p<0.05), but there were no significant differences in total protein (p>0.05). The result shows no significant difference in total protein level (p> 0.005)among the first trimester pregnant women when compared to the control subjects. It also shows no any significant difference in total protein level (p> 0.005) among the third trimester pregnant women when compared to the control subjects. Conclusion: There is reduction or decrease in calcium and albumin levels in pregnant women especially in the third trimester. Key words: Pregnancy; Total Protein; Albumin; Calciu

Photo induced ionization dynamics of the nitrogen vacancy defect in diamond investigated by single shot charge state detection

The nitrogen-vacancy centre (NV) has drawn much attention for over a decade, yet detailed knowledge of the photophysics needs to be established. Under typical conditions, the NV can have two stable charge states, negative (NV-) or neutral (NV0), with photo induced interconversion of these two states. Here, we present detailed studies of the ionization dynamics of single NV centres in bulk diamond at room temperature during illumination in dependence of the excitation wavelength and power. We apply a recent method which allows us to directly measure the charge state of a single NV centre, and observe its temporal evolution. Results of this work are the steady state NV- population, which was found to be always < 75% for 450 to 610 nm excitation wavelength, the relative absorption cross-section of NV- for 540 to 610 nm, and the energy of the NV- ground state of 2.6 eV below the conduction band. These results will help to further understand the photo-physics of the NV centre.Comment: 9 pages, 7 figure

Low Temperature Studies of Charge Dynamics of Nitrogen-Vacancy Defect in Diamond

In this paper, we study the photoinduced switching of the nitrogen-vacancy (NV) center between two different charge states - negative (NV-) and neutral (NV0) at liquid helium temperature. The conversion of NV- to NV0 on a single defect is experimentally proven and its rate scales quadratically with power under resonant excitation. In addition, we found that resonant excitation of the neutral NV changes the charge state, recovering its negative configuration. This type of conversion significantly improves spectral stability of NV- defect and allows high fidelity initialization of the spin qubit. A possible mechanism for ionization and recovery of the NV- defect is discussed. This study provides better understanding of the charge dynamics of the NV center, which is relevant for quantum information processing based on NV defect in diamond.Comment: 5 pages, 4 figure

Structure and vibrational spectra of carbon clusters in SiC

The electronic, structural and vibrational properties of small carbon interstitial and antisite clusters are investigated by ab initio methods in 3C and 4H-SiC. The defects possess sizable dissociation energies and may be formed via condensation of carbon interstitials, e.g. generated in the course of ion implantation. All considered defect complexes possess localized vibrational modes (LVM's) well above the SiC bulk phonon spectrum. In particular, the compact antisite clusters exhibit high-frequency LVM's up to 250meV. The isotope shifts resulting from a_{13}C enrichment are analyzed. In the light of these results, the photoluminescence centers D_{II} and P-U are discussed. The dicarbon antisite is identified as a plausible key ingredient of the D_{II}-center, whereas the carbon split-interstitial is a likely origin of the P-T centers. The comparison of the calculated and observed high-frequency modes suggests that the U-center is also a carbon-antisite based defect.Comment: 15 pages, 6 figures, accepted by Phys. Rev.

Defects in SiO2 as the possible origin of near interface traps in the SiC∕SiO2 system: A systematic theoretical study

A systematic study of the level positions of intrinsic and carbon defects in SiO2 is presented, based on density functional calculations with a hybrid functional in an alpha-quartz supercell. The results are analyzed from the point of view of the near interface traps (NIT), observed in both SiC/SiO2 and Si/SiO2 systems, and assumed to have their origins in the oxide. It is shown that the vacancies and the oxygen interstitial can be excluded as the origin of such NIT, while the silicon interstitial and carbon dimers give rise to gap levels in the energy range inferred from experiments. The properties of these defects are discussed in light of the knowledge about the SiC/SiO2 interface