555 research outputs found
Evidence for Thermally Activated Spontaneous Fluxoid Formation in Superconducting Thin-Film Rings
We have observed spontaneous fluxoid generation in thin-film rings of the
amorphous superconductor MoSi, cooled through the normal-superconducting
transition, as a function of quench rate and externally applied magnetic field,
using a variable sample temperature scanning SQUID microscope. Our results can
be explained using a model of freezout of thermally activated fluxoids,
mediated by the transport of bulk vortices across the ring walls. This
mechanism is complementary to a mechanism proposed by Kibble and Zurek, which
only relies on causality to produce a freezout of order parameter fluctuations.Comment: 4 pages, 3 figure
Are there static texture?
We consider harmonic maps from Minkowski space into the three sphere. We are
especially interested in solutions which are asymptotically constant, i.e.
converge to the same value in all directions of spatial infinity. Physical
3-space can then be compactified and can be identified topologically (but not
metrically!) with a three sphere. Therefore, at fixed time, the winding of the
map is defined. We investigate whether static solutions with non-trivial
winding number exist. The answer which we can proof here is only partial: We
show that within a certain family of maps no static solutions with non-zero
winding number exist. We discuss the existing static solutions in our family of
maps. An extension to other maps or a proof that our family of maps is
sufficiently general remains an open problem.Comment: 12 page Latex file, 1 postscript figure, submitted to PR
Piezoresistive Free‐standing Microfiber Strain Sensor for High‐resolution Battery Thickness Monitoring
Highly sensitive microfiber strain sensors are promising for the detection of mechanical deformations in applications where limited space is available. In particular for in situ battery thickness monitoring where high resolution and low detection limit are key requirements. Herein, the realization of a highly sensitive strain sensor for in situ lithium-ion (Li-ion) battery thickness monitoring is presented. The compliant fiber-shaped sensor is fabricated by an upscalable wet-spinning method employing a composite of microspherical core-shell conductive particles embedded in an elastomer. The electrical resistance of the sensor changes under applied strain, exhibiting a high strain sensitivity and extremely low strain detection limit of 0.00005 with high durability of 10 000 cycles. To demonstrate the accuracy and ease of applicability of this sensor, the real-time thickness change of a Li-ion battery pouch cell is monitored during the charge and discharge cycles. This work introduces a promising approach with the least material complexity for soft microfiber strain gauges
Angle-dependence of the Hall effect in HgBa2CaCu2O6 thin films
Superconducting compounds of the family Hg-Ba-Ca-Cu-O have been the subject
of intense study since the current record-holder for the highest critical
temperature of a superconductor belongs to this class of materials. Thin films
of the compound with two adjacent copper-oxide layers and a critical
temperature of about 120 K were prepared by a two-step process that consists of
the pulsed-laser deposition of precursor films and the subsequent annealing in
mercury-vapor atmosphere. Like some other high-temperature superconductors,
Hg-Ba-Ca-Cu-O exhibits a specific anomaly of the Hall effect, a double-sign
change of the Hall coefficient close to the superconducting transition. We have
investigated this phenomenon by measurements of the Hall effect at different
angles between the magnetic field direction and the crystallographic c-axis.
The results concerning the upper part of the transition, where the first sign
change occurs, are discussed in terms of the renormalized fluctuation model for
the Hall conductivity, adapted through the field rescaling procedure in order
to take into account the arbitrary orientation of the magnetic field.Comment: to be published in Phys. Rev.
A 1.8 mJ, picosecond Nd:YVO4 bounce amplifier pump front-end system for high-accuracy XUV-frequency comb spectroscopy
1 mu s, providing a promising pump laser system for parametric amplification and subsequent upconversion of near-infrared frequency combs to the extreme ultraviolet (XUV). (C) 2012 by Astro, Ltd
Second wind of the Dulong-Petit Law at a quantum critical point
Renewed interest in 3He physics has been stimulated by experimental
observation of non-Fermi-liquid behavior of dense 3He films at low
temperatures. Abnormal behavior of the specific heat C(T) of two-dimensional
liquid 3He is demonstrated in the occurrence of a T-independent term in C(T).
To uncover the origin of this phenomenon, we have considered the group velocity
of transverse zero sound propagating in a strongly correlated Fermi liquid. For
the first time, it is shown that if two-dimensional liquid 3He is located in
the vicinity of the quantum critical point associated with a divergent
quasiparticle effective mass, the group velocity depends strongly on
temperature and vanishes as T is lowered toward zero. The predicted vigorous
dependence of the group velocity can be detected in experimental measurements
on liquid 3He films. We have demonstrated that the contribution to the specific
heat coming from the boson part of the free energy due to the transverse
zero-sound mode follows the Dulong-Petit Law. In the case of two-dimensional
liquid 3He, the specific heat becomes independent of temperature at some
characteristic temperature of a few mK.Comment: 5 pages, 1 figur
Label-free electrochemical DNA sensor using "click"-functionalized PEDOT electrodes
Here we describe a label-free electrochemical DNA sensor based on poly(3,4-ethylenedioxythiophene)-modified (PEDOT-modified) electrodes. An acetylene-terminated DNA probe, complementary to a specific "Hepatitis C" virus sequence, was immobilized onto azido-derivatized conducting PEDOT electrodes using "click" chemistry. DNA hybridization was then detected by differential pulse voltammetry, evaluating the changes in the electrochemical properties of the polymer produced by the recognition event. A limit of detection of 0.13. nM was achieved using this highly selective PEDOT-based genosensor, without the need for labeling techniques or microelectrode fabrication processes. These results are promising for the development of label-free and reagentless DNA hybridization sensors based on conducting polymeric substrates. Biosensors can be easily prepared using any DNA sequence containing an alkyne moiety. The data presented here reveal the potential of this DNA sensor for diagnostic applications in the screening of diseases, such as "Hepatitis C", and genetic mutations.The authors would like to thank the ICTS “NANBIOSIS”, more specifically to the
Nanotechnology Platform, unit of the Networking Biomedical Research Center in
Bioengineering, Biomaterials & Nanomedicine (CIBER-BBN) at the Institute for
Bioengineering of Catalonia (IBEC) and also to the Serveis Cientificotècnics (SCT) of the Universitat de Barcelona (UB) for their assistance in XPS and ToF-SIMS analyses. This work was supported by Networking Biomedical Research Center in Bioengineering, Biomaterials & Nanomedicine (CIBER-BBN), Spain. The Nanobioengineering group at IBEC receives support from the Spanish Ministry of
Science and Education and the Commission for Universities and Research of the Department of Innovation, Universities and Enterprise of the Generalitat de Catalunya (No. 2009 SGR 505). In addition, the research received support from the Spanish Ministry of Science and Education, CICYT (CTQ2009-07758), and the Fundación Botín, Santander, Spain.Peer reviewe
Electronic structure and excited state dynamics in a dicyanovinyl-substituted oligothiophene on Au(111)
Dicyanovinyl (DCV)-substituted oligothiophenes are promising donor materials
in vacuum-processed small-molecule organic solar cells. Here, we studied the
structural and the electronic properties of DCV-dimethyl-pentathiophene
(DCV5T-Me2) adsorbed on Au(111) from submonolayer to multilayer coverages.
Using a multi-technique experimental approach (low-temperature scanning
tunneling microscopy/spectroscopy (STM/STS), atomic force microscopy (AFM),
and two-photon photoemission (2PPE) spectroscopy), we determined the energetic
position of several affinity levels as well as ionization potentials
originating from the lowest unoccupied molecular orbitals (LUMO) and the
highest occupied molecular orbitals (HOMO), evidencing a transport gap of 1.4
eV. Proof of an excitonic state was found to be a spectroscopic feature
located at 0.6 eV below the LUMO affinity level. With increasing coverage
photoemission from excitonic states gains importance. We were able to track
the dynamics of several electronically excited states of multilayers by means
of femtosecond time-resolved 2PPE. We resolved an intriguing relaxation
dynamics involving four processes, ranging from sub-picosecond (ps) to several
hundred ps time spans. These show a tendency to increase with increasing
coverage. The present study provides important parameters such as energetic
positions of transport levels as well as lifetimes of electronically excited
states, which are essential for designing organic-molecule-based
optoelectronic devices
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