30 research outputs found
Bolometric technique for high-resolution broadband microwave spectroscopy of ultra-low-loss samples
A novel low temperature bolometric method has been devised and implemented
for high-precision measurements of the microwave surface resistance of small
single-crystal platelet samples having very low absorption, as a continuous
function of frequency. The key to the success of this non-resonant method is
the in-situ use of a normal metal reference sample that calibrates the absolute
rf field strength. The sample temperature can be controlled independently of
the 1.2 K liquid helium bath, allowing for measurements of the temperature
evolution of the absorption. However, the instrument's sensitivity decreases at
higher temperatures, placing a limit on the useful temperature range. Using
this method, the minimum detectable power at 1.3 K is 1.5 pW, corresponding to
a surface resistance sensitivity of 1 for a typical 1
mm1 mm platelet sample.Comment: 13 pages, 12 figures, submitted to Review of Scientific Instrument
Phenomenology of a-axis and b-axis charge dynamics from microwave spectroscopy of highly ordered YBa2Cu3O6.50 and YBa2Cu3O6.993
Extensive measurements of the microwave conductivity of highly pure and
oxygen-ordered \YBCO single crystals have been performed as a means of
exploring the intrinsic charge dynamics of a d-wave superconductor. Broadband
and fixed-frequency microwave apparatus together provide a very clear picture
of the electrodynamics of the superconducting condensate and its thermally
excited nodal quasiparticles. The measurements reveal the existence of very
long-lived excitations deep in the superconducting state, as evidenced by sharp
cusp-like conductivity spectra with widths that fall well within our
experimental bandwidth. We present a phenomenological model of the microwave
conductivity that captures the physics of energy-dependent quasiparticle
dynamics in a d-wave superconductor which, in turn, allows us to examine the
scattering rate and oscillator strength of the thermally excited quasiparticles
as functions of temperature. Our results are in close agreement with the
Ferrell-Glover-Tinkham sum rule, giving confidence in both our experiments and
the phenomenological model. Separate experiments for currents along the and directions of detwinned crystals allow us to isolate the role
of the CuO chain layers in \YBCO, and a model is presented that incorporates
both one-dimensional conduction from the chain electrons and two-dimensional
transport associated with the \cuplane plane layers.Comment: 17 pages, 13 figure
Stability of nodal quasiparticles in underdoped YBa2Cu3O6+y probed by penetration depth and microwave spectroscopy
High resolution measurements of superfluid density and broadband
quasiparticle conductivity have been used to probe the low energy excitation
spectrum of nodal quasiparticles in underdoped YBCO. Penetration depth is
measured to temperatures as low as 0.05 K. Microwave conductivity is measured
from 0.1 to 20 GHz and is a direct probe of zero-energy quasiparticles. The
data are compared with predictions for a number of theoretical scenarios that
compete with or otherwise modify pure d-wave superconductivity, in particular
commensurate and incommensurate spin and charge density waves; d + i s and d +
i d superconductivity; circulating current phases; and the BCS--BEC crossover.
We conclude that the data are consistent with a pure d-wave state in the
presence of a small amount of strong scattering disorder, and are able to rule
out most candidate competing states either completely, or to a level set by the
energy scale of the disorder, ~ 4 K. Commensurate spin and charge density
orders, however, are not expected to alter the nodal spectrum and therefore
cannot be excluded
Stability of nodal quasiparticles in underdoped YBa2Cu3O6+y probed by penetration depth and microwave spectroscopy
High resolution measurements of superfluid density and broadband
quasiparticle conductivity have been used to probe the low energy excitation
spectrum of nodal quasiparticles in underdoped YBCO. Penetration depth is
measured to temperatures as low as 0.05 K. Microwave conductivity is measured
from 0.1 to 20 GHz and is a direct probe of zero-energy quasiparticles. The
data are compared with predictions for a number of theoretical scenarios that
compete with or otherwise modify pure d-wave superconductivity, in particular
commensurate and incommensurate spin and charge density waves; d + i s and d +
i d superconductivity; circulating current phases; and the BCS--BEC crossover.
We conclude that the data are consistent with a pure d-wave state in the
presence of a small amount of strong scattering disorder, and are able to rule
out most candidate competing states either completely, or to a level set by the
energy scale of the disorder, ~ 4 K. Commensurate spin and charge density
orders, however, are not expected to alter the nodal spectrum and therefore
cannot be excluded
Absolute values of the London penetration depth in YBa2Cu3O6+y measured by zero field ESR spectroscopy on Gd doped single crystals
Zero-field electron spin resonance (ESR) of dilute Gd ions substituted for Y
in the cuprate superconductor YBaCuO is used as a novel
technique for measuring the absolute value of the low temperature magnetic
penetration depth . The Gd ESR spectrum of samples with
substitution was obtained with a broadband microwave technique
that measures power absorption bolometrically from 0.5 GHz to 21 GHz. This ESR
spectrum is determined by the crystal field that lifts the level degeneracy of
the spin 7/2 Gd ion and details of this spectrum provide information
concerning oxygen ordering in the samples. The magnetic penetration depth is
obtained by relating the number of Gd ions exposed to the microwave magnetic
field to the frequency-integrated intensity of the observed ESR transitions.
This technique has allowed us to determine precise values of for
screening currents flowing in the three crystallographic orientations (, and ) in samples of GdYBaCuO of three different oxygen contents ( K), ( K) and
( K). The in-plane values are found to depart substantially from the
widely reported relation .Comment: 14 pages, 12 figures; version to appear in PR
Tumour-associated carbohydrate antigens in breast cancer
Glycosylation changes that occur in cancer often lead to the expression of tumour-associated carbohydrate antigens. In breast cancer, these antigens are usually associated with a poor prognosis and a reduced overall survival. Cellular models have shown the implication of these antigens in cell adhesion, migration, proliferation and tumour growth. The present review summarizes our current knowledge of glycosylation changes (structures, biosynthesis and occurrence) in breast cancer cell lines and primary tumours, and the consequences on disease progression and aggressiveness. The therapeutic strategies attempted to target tumour-associated carbohydrate antigens in breast cancer are also discussed
Critical twisting torque in case of I-beams, cut at the base
W artykule przedstawiono wyniki badań teoretycznych podcięcia belek dwuteowych przy podporach na wartości momentu krytycznego zwichrzenia, tym samym na nośność belek na zginanie. Przeanalizowano zwichrzenie typowych belek dwuteowych dla różnych rodzajów głębokości i długości podcięć. Uwzględniono różne rodzaje obciążeń i zmianę ich ustawień na wysokości i przekroju. Obliczenia wykonano przy pomocy programu SOFiSTiK odpowiednio modelując strefy podporowe belek. Wyniki analiz przedstawiono na wykresach.The article presents results of theoretical research regarding undercutting of I-beams at the base, for the values of critical twisting torque, and beam capacity within the scope of bending. The analyzed twists of typical I-beams has been considered for several depths and lengths of the undercuts. A variety of load types has been taken into account, as well variability in their position – both in height, as well as in crosssections. Calculations have been executed with the use of SOF iST iK software bundle, which modeled the support zones of the beams. Results of the analysis have been presented by the charts