2,064 research outputs found
Defect-unbinding and the Bose-glass transition in layered superconductors
The low-field Bose-glass transition temperature in heavy-ion irradiated
Bi_2Sr_2CaCu_2O_8+d increases progressively with increasing density of
irradiation-induced columnar defects, but saturates for densities in excess of
1.5 x10^9 cm^-2. The maximum Bose-glass temperature corresponds to that above
which diffusion of two-dimensional pancake vortices between different vortex
lines becomes possible, and above which the ``line-like'' character of vortices
is lost. We develop a description of the Bose-glass line that is in excellent
quantitative agreement with the experimental line obtained for widely different
values of track density and material parameters.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Let
Bloch oscillations with a metastable helium Bose-Einstein condensate
We have observed Bloch oscillations of a 4He∗ Bose-Einstein condensate in an optical lattice at 1557.3 nm. Due to its low mass, metastable helium was efficiently accelerated orders of magnitude faster than demonstrated with other atoms. In a horizontal lattice, we could transfer a total of 800ℏk of momentum by shuttling the atomic cloud back and forth 50 times between the 4 k and -4 k momentum states with an efficiency of over 99% per Bloch cycle. In a vertical lattice, gravity-induced Bloch oscillations were demonstrated, from which the local gravitational acceleration was derived with a statistical uncertainty of 4×10-5. A clear advantage of He∗ over other atoms is that it can be detected with a microchannel plate detector with near unity efficiency, and this enabled observation of Bloch oscillations up to 12 s even though the number of atoms decreased by three orders of magnitude. These results establish He∗ as a promising candidate for future precision measurements with atom interferometry
Моделювання процесу обробки на фрезерному верстаті 6Р13Ф3 та прогнозування показників процесу стружкоутворення
Розроблено методологію побудови раціональної з точки зору витрат ресурсів обчислювальної системи скінчено-елементної сітки складної технологічної системи, що включає елементи різної маси, жорсткості та розмірів, а також рухомі та нерухомі з’єднання зі скінченою величиною контактної жорсткості. Проведені пошукові розрахунки процесу стружкоутворення у абсолютно жорсткій та податливій технологічній системах, результати яких показали, що переміщення у технологічній системі в момент врізання призводять до запізнення початку сталого стружкоутворення, додаткового тертя зубів о заготовку без різання та активації вібрацій.
При цитуванні документа, використовуйте посилання http://essuir.sumdu.edu.ua/handle/123456789/2685
Supercooling of the disordered vortex lattice in Bi_2Sr_2CaCu_2O_8+d
Time-resolved local induction measurements near to the vortex lattice
order-disorder transition in optimally doped
BiSrCaCuO single crystals shows that the
high-field, disordered phase can be quenched to fields as low as half the
transition field. Over an important range of fields, the electrodynamical
behavior of the vortex system is governed by the co-existence of the two phases
in the sample. We interpret the results in terms of supercooling of the
high-field phase and the possible first order nature of the order-disorder
transition at the ``second peak''.Comment: 4 pages, 3 figures. Submitted to Nature, July 10th, 1999; Rejected
August 8th for lack of broad interest Submitted to Physical Review Letters
September 10th, 199
Vortex fluctuations in underdoped Bi2Sr2CaCu2O8+d crystals
Vortex thermal fluctuations in heavily underdoped Bi2Sr2CaCu2O8+d (Tc=69.4 K)
are studied using Josephson plasma resonance (JPR). From the data in zero
magnetic field, we obtain the penetration depth along the c-axis,
lambda_{L,c}(0) = 229 micrometers and the anisotropy ratio gamma(0) = 600. The
low plasma frequency allows us to study phase correlations over the whole
vortex solid (Bragg-glass) state. The JPR results yield a wandering length
r_{w} of vortex pancakes. The temperature dependence of r_{w} as well as its
increase with applied dc magnetic field can only be explained by the
renormalization of the tilt modulus by thermal fluctuations, and suggest the
latter is responsible for the dissociation of the vortices at the first order
transition.Comment: 4 pages, 5 figures. Submitted to Phys. Rev. Let
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