Preparation and properties of all high Tc SNS-type edge DC SQUIDs

High-Tc SNS-type Josephson junctions and DC SQUIDs were successfully fabricated using hetero-epitaxially grown multilayers of YBa2Cu3Ox and PrBa2 Cu3O. These layers are c-axis oriented, and hence edges of the multilayers give rise to a current flow in the ab-plane between the electrodes of a Josephson junction. The necessary structuring was done by Ar ion beam etching. The individual junctions exhibit a supercurrent up to 80 K. The IcRn product of these junctions usually has a lower limit of 8 mV at 4.2 K. Voltage modulation of the first DC SQUIDs can be observed up to 66 K. The voltage modulation for various bias currents investigated at 4.2 K noise measurements were performed. Details on the fabrication and measurements are presente

Conductance studies on different types of Nb/Al, AlOx,(/A1)/Nb Josephson tunnel junctions

The conductance-voltage characteristics of different types of Josephson tunnel junctions have been measured at 4.2 K: symmetric Nb/Al, AlOx/Al/Nb, asymmetric Nb/Al, AlOx/Nb and Nb/Al/AlOx-/AlOx/Nb, containing a double oxidation layer. The symmetric junctions can be described very well by a trapezoidal potential barrier model. The asymmetric junctions show less agreement with theory. In these junctions resistance switching occurs, possibly due to charge trapping. The resistance is lower than in symmetric junctions. The conductance measurements on double oxidation layer junctions show, that this type of junction has an inhomogeneous oxide layer

Multichannel heart scanner based on high-Tc SQUIDs

A 7-channel magnetometer for magnetocardiography based on high-T c SQUIDs has been realized. This magnetometer is used for test experiments in the development of a multichannel high-Tc SQUID based heart-scanner for clinical applications. The intrinsic noise level of the channels in the 7-channel system is typically 120 fT/¿(Hz) down to 1 Hz. Magnetocardiograms were recorded inside a magnetically shielded room. Introductory experiments were performed on the suppression of noise by combining magnetometers to form planar gradiometers. The noise suppression that can be established appeared to be limited by the imbalance of the gradiometric configuration, which is roughly 2%. This relatively poor balance of the system is caused by inaccuracies in the transfer functions of the individual SQUID magnetometers, and by deviations from the planar geometr

AdS-Carroll Branes

Coset methods are used to determine the action of a co-dimension one brane (domain wall) embedded in (d+1)-dimensional AdS space in the Carroll limit in which the speed of light goes to zero. The action is invariant under the non-linearly realized symmetries of the AdS-Carroll spacetime. The Nambu-Goldstone field exhibits a static spatial distribution for the brane with a time varying momentum density related to the brane's spatial shape as well as the AdS-C geometry. The AdS-C vector field dual theory is obtained.Comment: 47 page

Josephson junctions and DC SQUIDS based on Nb/Al technology

A process for fabricating high-quality Josephson junctions and DC SQUIDS on basis of Nb/Al technology has been developed. DC magnetron sputtering is used for the deposition of the metal layers and the barrier is formed by thermal oxidation of the Al-layer. The junction area of 5 µm × 5 5 µm is obtained using anodisation. Three types of Josephson tunnel junctions have been prepared: standard Nb/Al, AlOx/Nb, symmetric Nb/Al, AlOx, Al/Nb and Nb/Al, AlOx/AlOx/Nb, the latter having a double oxide layer. We performed current-voltage and conductance-voltage measurements at different temperatures and special attention was paid to the noise behaviour. Gap and sub-gap parameters as well as barrier parameters are presented. Three different DC SQUID configurations were developed on basis of the Nb/Al Josephson junctions. The measured characteristics of the standard Tesche-Clarke DC SQUID, the resistively shunted SQUID and the inductively shunted SQUID are compared with special attention being paid to the noise properties. A 19-channel DC SQUID magnetometer with standard and/or resistively-shunted DC SQUIDs is under construction

Towards String Predictions

The aim of superstring phenomenology is to develop the tools and methodology needed to confront string theory with experimental data. The first mandatory task is to find string solutions which reproduce the observable data. The subsequent goal is to extract potential signatures beyond the observable data. Recently, by studying exact flat directions of non-Abelian singlet fields, we demonstrated the existence of free fermionic heterotic-string models in which the $SU(3)\times SU(2)\times U(1)_Y$-charged matter spectrum, just below the string scale, consists solely of the MSSM spectrum. In this paper we study the possibility that the exact flat directions leave a $U(1)_{Z^\prime}$ symmetry unbroken at the Planck scale. We demonstrate in a specific example that such unbroken $U(1)_{Z^\prime}$ is in general expected to be not of the GUT type but of intrinsic stringy origin. We study its phenomenological characteristics and the consequences in the case that $U(1)_{Z^\prime}$ remains unbroken down to low energies. We suggest that observation in forthcoming colliders of a $Z^\prime$, with universal couplings for the two light generations but different couplings for the heavy generation may provide evidence for the $Z_2\times Z_2$ orbifold which underlies the free fermionic models.Comment: 18 pages. Standard Latex. References adde

The Low Energy Behavior of some Models with Dynamical Supersymmetry Breaking

We study supersymmetric SU(5) chiral gauge theories with 2 fields in the 10 representation, $2+N_F$ fields in the $\bar{5}$ representation and $N_F$ fields in the 5 representation, for $N_F=0,1,2$. With a suitable superpotential, supersymmetry is shown to be broken dynamically for each of these values of $N_F$. We analyze the calculable limit for the model with $N_F=0$ in detail, and determine the low energy effective sigma model in this case. For $N_F=1$ we find the quantum moduli space, and for $N_F=2$ we construct the s--confining potential.Comment: 16 page

Investigating the KNDy hypothesis in humans by co-administration of kisspeptin, neurokinin B and naltrexone in men

Context: A subpopulation of hypothalamic neurons co-localise three neuropeptides namely kisspeptin, neurokinin B (NKB) and dynorphin collectively termed KNDy neurons. Animal studies suggest they interact to affect pulsatile GnRH release (KNDy hypothesis); kisspeptin stimulates, NKB modulates and dynorphin (an opioid) inhibits. Objective: To investigate the KNDy hypothesis in humans, we assessed for the first time the effects of co-administration of kisspeptin-54, NKB and an opioid receptor antagonist, naltrexone on LH pulsatility (surrogate marker for GnRH pulsatility) and gonadotropin release. Design, setting and participants: Ethically approved prospective, single-blinded placebo-controlled study. Healthy male volunteers (n=5/group) attended our research facility for 8 study visits. Intervention and main outcome measure: After 1h baseline blood sampling, participants received a different intervention at each visit: oral 50mg naltrexone (NAL), 8h intravenous infusions of vehicle, 2.56nmol/kg/h NKB (NKB), 0.1nmol/kg/h kissspeptin-54 (KP) alone and in combination. Frequent blood sampling to measure plasma gonadotropins and sex steroids was conducted and LH pulsatility was determined using blinded deconvolution analysis. Results: All kisspeptin and naltrexone containing groups potently increased LH and LH pulsatility (p<0.001 vs vehicle). NKB alone did not affect gonadotropins. NKB+KP had significantly lower increases in gonadotropins compared with kisspeptin alone (p<0.01). NAL+KP was the only group to significantly increase LH pulse amplitude (p<0.001 vs vehicle). Conclusions: Our results suggest significant interactions between the KNDy neuropeptides on LH pulsatility and gonadotropin release in humans. This has important implications for improving our understanding of GnRH pulse generation in humans