60 research outputs found
1D Quantum transport in the even-chain spin-ladder compound Sr2.5Ca11.5Cu24O41 and YBa2Cu4O8
The temperature dependence of the resistivity r(T) of the novel
Sr2.5Ca11.5Cu24O41 ladder compound under hydrostatic pressure of up to 8 GPa
has been explained by assuming that the relevant length scale for electrical
transport is given by the magnetic correlation length related to the opening of
a spin-gap in a 1D even-chain spin-ladder (1D-SL). The pressure dependence of
the gap was extracted by applying this model to r(T) data obtained at different
pressures. The r(T) dependence of the underdoped cuprate YBa2Cu4O8 demonstrates
a remarkable scaling with the r(T) of the 1D-SL compound Sr2.5Ca11.5Cu24O41.
This scaling implies that underdoped cuprates at Tc < T < T* are in the 1D
regime and their pseudo-gap below T* is the spin-gap in the even-chain 1D-SL
formed at T < T* in these materials.Comment: 10 pages, all PDF, contribution to Europhys.Lett.
Flux Jumps Driven by a Pulsed Magnetic Field
The understanding of flux jumps in the high temperature superconductors is of
importance since the occurrence of these jumps may limit the perspectives of
the practical use of these materials. In this work we present the experimental
study of the role of heavy ion irradiation in stabilizing the HTSC against flux
jumps by comparing un-irradiated and 7.5 10^10 Kr-ion/cm2 irradiated
(YxTm1-x)Ba2Cu3O7 single crystals. Using pulsed field magnetization
measurements, we have applied a broad range of field sweep rates from 0.1T/s up
to 1800 T/s to investigate the behavior of the flux jumps. The observed flux
jumps, which may be attributed to thermal instabilities, are incomplete and
have different amplitudes. The flux jumps strongly depend on the magnetic
field, on the magneto-thermal history of the sample, on the magnetic field
sweep rate, on the critical current density jc, on the temperature and on the
thermal contact with the bath in which the sample is immersed.Comment: 5 pages, PDF-fil
Coherent control of nuclear spin isomers of molecules: The role of molecular motion
Molecular center-of-mass motion is taken into account in the theory of
coherent control of nuclear spin isomers of molecules. It is shown that
infrared radiation resonant to the molecular rovibrational transition can
substantially enrich nuclear spin isomers and speed up their conversion rate.Comment: REVTEX, 13 pages + 3 eps figure
Normal State Resistivity of Underdoped YBa2Cu3Ox Thin Films and La2-xSrxCuO4 Ultra-Thin Films under Epitaxial Strain
The normal state resistivity of high temperature superconductors can be
probed in the region below Tc by suppressing the superconducting state in high
magnetic fields. Here we present the normal state properties of YBa2Cu3Ox thin
films in the underdoped regime and the normal state resistance of La2-xSrxCuO4
thin films under epitaxial strain, measured below Tc by applying pulsed fields
up to 60 T. A universal rho(T) behaviour is reported. We interpret these data
in terms of the recently proposed 1D quantum transport model with the 1D paths
corresponding to the charge stripes.Comment: 5 pages, PDF and PS, including figures, presented at MOS99 and
accepted for publication in J. of Low Temp. Phy
Gastrointestinal complications of accidental ingestion of foreign objects
Ingestion of foreign objects is common and most of the time, they pass without major problems. However sometimes they could cause significant morbidity or even mortality. Most of the time they cause pain in the pharyngeal or oesophageal area. In these instants, diagnosing the problem is straightforward, limiting the use of radiographic diagnosis.However the intraperitoneal complications include stomach or bowel perforation, obstruction, abscedation, septicemia or even hemorrhage or thrombosis of the abdominal veins. Because of the considerable risks, accompanied by the accidental ingestion of a metallic object, the preferred technique for screening is still Computed Tomography. However not all of these objects are radio-opaque and therefore could not always be diagnosed radiographically. In this article we will describe several cases of complications, due to the accidental ingestion of foreign objects. Also we will describe certain patient related risk factors significantly increasing, not only the amount, but also the severity of those complications. Diverticulosis seems the most common risk factor amongst the patients described and so it could be one of the more common triggers causing (recidivating) diverticulitis attacks. But because not all of the ingested foreign objects are radiopaque or still in the gastrointestinal tract, such a theory is difficult to prove
Critical Currents, Pinning Forces and Irreversibility Fields in (YxTml-x)Ba2Cu3O7 Single Crystals with Columnar Defects in Fields up to 50 T
We have studied the influence of columnar defects, created by heavy-ion (Kr)
irradiation with doses up to 6 10^11 Kr-ions/cm2, on the superconducting
critical parameters of single crystalline (YxTm1-x)Ba2Cu3O7. Magnetisation
measurements in pulsed fields up to 50 T in the temperature range 4.2 - 90 K
revealed that: (i) in fields up to T the critical current Jc(H,T) is
considerably enhanced and (ii) down to temperatures T ~ 40 K the
irreversibility field Hirr(T) is strongly increased. The field range and
magnitude of the Jc(H,T) and Hirr(T) enhancement increase with increasing
irradiation dose. To interpret these observations, an effective matching field
was defined. Moreover, introducing columnar defects also changes the pinning
force fp qualitatively. Due to stronger pinning of flux lines by the amorphous
defects, the superconducting critical parameters largely exceed those
associated with the defect structures in the unirradiated as-grown material:
Jc,irrad(77 K, 5 T) ^3 10* Jc,ref(77 K, 5 T).Comment: 11 pages, all PDF, contribution to Physica
Enrichment of CH3F nuclear spin isomers by resonant microwave radiation
Theoretical model of the coherent control of nuclear spin isomers by
microwave radiation has been developed. Model accounts the M-degeneracy of
molecular states and molecular center-of-mass motion. The model has been
applied to the 13CH3F molecules. Microwave radiation excites the para state
(J=11,K=1) which is mixed by the nuclear spin-spin interaction with the ortho
state (9,3). Dependencies of the isomer enrichment and conversion rates on the
radiation frequency have been calculated. Both spectra consist of two
resonances situated at the centers of allowed and forbidden (by nuclear spin)
transitions in the molecule. Larger enrichment, up to 7%, can be produced by
strong radiation resonant to the forbidden transition. The spin conversion rate
can be increased by 2 orders of magnitude at this resonance.Comment: REVTEX, 14 pages + 6 eps figure
On bi-skew braces and brace blocks
L. N. Childs defined a bi-skew brace to be a skew brace such that if we swap the role of the two operations, then we find again a skew brace. In this paper, we give a systematic analysis of bi-skew braces. We study nilpotency and solubility, and connections between bi-skew braces and set-theoretic solutions of the Yang–Baxter equation. Further, we deal with Byott's conjecture in the case of bi-skew braces, and we use bi-skew braces as a tool to solve a classification problem proposed by L. Vendramin. In the final part, we investigate brace blocks, defined by A. Koch to be families of group operations on a given set such that any two of them yield a bi-skew brace. We provide a characterisation of brace blocks, illustrate how all known constructions in literature follow in a natural way from our characterisation, and give several new examples
On the connection between Hopf--Galois structures and skew braces
We present a different point of view on the well-known connection between
Hopf--Galois structures and skew braces, building on a recent paper of A. Koch
and P. J. Truman.
We show that the known results which involve this connection easily carry
over to this new perspective, and that new ones naturally appear.
As an application, we present new insights on the study of the surjectivity
of the Hopf--Galois correspondence, explaining in more detail the role of
bi-skew braces in Hopf--Galois theory.Comment: 20 page
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