Determination of characteristic relaxation times and their significance in glassy disordered insulators

We revisit the field effect procedure used to characterise the slow dynamics of glassy Anderson insulators. It is shown that in the slowest systems the procedure fails and the "characteristic" time values extracted are not intrinsic but determined by the experimental procedure itself. In other cases (like lightly doped indium oxide) qualitative indications about the dynamics might be obtained, however the times extracted cannot be seen as characteristic relaxation times of the system in any simple manner, and more complete experiments are necessary. Implications regarding the effect of carrier concentration on the emergence of glassiness are briefly outlined.Comment: published with minor proof correction

Idiopathic True Aneurysm of the Radial Artery: A Rare Entity

AbstractIntroductionTrue aneurysms of the radial artery are extremely rare. Most cases of Radial artery aneurysm are the result of iatrogenic trauma, however other rare causes such as vascular tumours, connective tissue diseases and occupational injury have also been reported.Case reportA 60-year-old man presented with a pulsating mass in the anatomical snuffbox of the left hand. He underwent distal radial artery ligation and excision of the aneurysm. Histopathology demonstrated this to be a true aneurysm in continuation with the vessel wall.DiscussionThere are only a few cases of true distal radial artery aneurysm described in the literature. Careful examination and pre-operative imaging will help determine the most appropriate surgical management, including the need for vascular reconstruction

Absence of weak antilocalization in ferromagnetic films

We present magnetoresistance measurements performed on ultrathin films of amorphous Ni and Fe. In these films the Curie temperature drops to zero at small thickness, making it possible to study the effect of ferromagnetism on localization. We find that non-ferromagnetic films are characterized by positive magnetoresistance. This is interpreted as resulting from weak antilocalization due to strong Bychkov-Rashba spin orbit scattering. As the films become ferromagnetic the magnetoresistance changes sign and becomes negative. We analyze our data to identify the individual contributions of weak localization, weak antilocalization and anisotropic magnetoresistance and conclude that the magnetic order suppresses the influence of spin-orbit effects on localization phenomena in agreement with theoretical predictions.Comment: 6 pages, 6 figure

Universal transport in 2D granular superconductors

The transport properties of quench condensed granular superconductors are presented and analyzed. These systems exhibit transitions from insulating to superconducting behavior as a function of inter-grain spacing. Superconductivity is characterized by broad transitions in which the resistance drops exponentially with reducing temperature. The slope of the log R versus T curves turns out to be universaly dependent on the normal state film resistance for all measured granular systems. It does not depend on the material, critical temperature, geometry, or experimental set-up. We discuss possible physical scenarios to explain these findings.Comment: 4 pages, 3 figure

Is a multiple excitation of a single atom equivalent to a single excitation of an ensemble of atoms?

Recent technological advances have enabled to isolate, control and measure the properties of a single atom, leading to the possibility to perform statistics on the behavior of single quantum systems. These experiments have enabled to check a question which was out of reach previously: Is the statistics of a repeatedly excitation of an atom N times equivalent to a single excitation of an ensemble of N atoms? We present a new method to analyze quantum measurements which leads to the postulation that the answer is most probably no. We discuss the merits of the analysis and its conclusion.Comment: 3 pages, 3 figure

Ulta-slow relaxation in discontinuous-film based electron glasses

We present field effect measurements on discontinuous 2D thin films which are composed of a sub monolayer of nano-grains of Au, Ni, Ag or Al. Like other electron glasses these systems exhibit slow conductance relaxation and memory effects. However, unlike other systems, the discontinuous films exhibit a dramatic slowing down of the dynamics below a characteristic temperature $T^*$. $T^*$ is typically between 10-50K and is sample dependent. For $T<T^*$ the sample exhibits a few other peculiar features such as repeatable conductance fluctuations in millimeter size samples. We suggest that the enhanced system sluggishness is related to the current carrying network becoming very dilute in discontinuous films so that the system contains many parts which are electrically very weakly connected and the transport is dominated by very few weak links. This enables studying the glassy properties of the sample as it transitions from a macroscopic sample to a mesocopic sample, hence, the results provide new insight on the underlying physics of electron glasses.Comment: 4 pages, 4 figure

Niobium superconducting nanowire single-photon detectors

We investigate the performance of superconducting nanowire photon detectors fabricated from ultra-thin Nb. A direct comparison is made between these detectors and similar nanowire detectors fabricated from NbN. We find that Nb detectors are significantly more susceptible than NbN to thermal instability (latching) at high bias. We show that the devices can be stabilized by reducing the input resistance of the readout. Nb detectors optimized in this way are shown to have approximately 2/3 the reset time of similar large-active-area NbN detectors of the same geometry, with approximately 6% detection efficiency for single photons at 470 nm

Reset dynamics and latching in niobium superconducting nanowire single-photon detectors

We study the reset dynamics of niobium (Nb) superconducting nanowire single-photon detectors (SNSPDs) using experimental measurements and numerical simulations. The numerical simulations of the detection dynamics agree well with experimental measurements, using independently determined parameters in the simulations. We find that if the photon-induced hotspot cools too slowly, the device will latch into a dc resistive state. To avoid latching, the time for the hotspot to cool must be short compared to the inductive time constant that governs the resetting of the current in the device after hotspot formation. From simulations of the energy relaxation process, we find that the hotspot cooling time is determined primarily by the temperature-dependent electron-phonon inelastic time. Latching prevents reset and precludes subsequent photon detection. Fast resetting to the superconducting state is therefore essential, and we demonstrate experimentally how this is achieved

Chemical cross-linking/mass spectrometry targeting acidic residues in proteins and protein complexes

The study of proteins and protein complexes using chemical cross-linking followed by the MS identification of the cross-linked peptides has found increasingly widespread use in recent years. Thus far, such analyses have used almost exclusively homobifunctional, amine-reactive cross-linking reagents. Here we report the development and application of an orthogonal cross-linking chemistry specific for carboxyl groups. Chemical cross-linking of acidic residues is achieved using homobifunctional dihydrazides as cross-linking reagents and a coupling chemistry at neutral pH that is compatible with the structural integrity of most protein complexes. In addition to cross-links formed through insertion of the dihydrazides with different spacer lengths, zero-length cross-link products are also obtained, thereby providing additional structural information. We demonstrate the application of the reaction and the MS identification of the resulting cross-linked peptides for the chaperonin TRiC/CCT and the 26S proteasome. The results indicate that the targeting of acidic residues for cross-linking provides distance restraints that are complementary and orthogonal to those obtained from lysine cross-linking, thereby expanding the yield of structural information that can be obtained from cross-linking studies and used in hybrid modeling approaches