140 research outputs found
Vortex pinning and flux flow microwave studies of coated conductors
Demanding microwave applications in a magnetic field require the material
optimization not only in zero-field but, more important, in the in-field flux
motion dominated regime. However, the effect of artificial pinning centers
(APC) remains unclear at high frequency. Moreover, in coated conductors the
evaluation of the high frequency material properties is difficult due to the
complicated electromagnetic problem of a thin superconducting film on a
buffered metal substrate. In this paper we present an experimental study at 48
GHz of 150-200 nm YBaCuO coated conductors, with and without
APCs, on buffered Ni-5at%W tapes. By properly addressing the electromagnetic
problem of the extraction of the superconductor parameters from the measured
overall surface impedance , we are able to extract and to comment on the
London penetration depth, the flux flow resistivity and the pinning constant,
highlighting the effect of artificial pinning centers in these samples.Comment: 5 pages, IEEE Trans. Appl. Supercond., accepted for publication
(2019
The Lasso with general Gaussian designs with applications to hypothesis testing
The Lasso is a method for high-dimensional regression, which is now commonly
used when the number of covariates is of the same order or larger than the
number of observations . Classical asymptotic normality theory is not
applicable for this model due to two fundamental reasons: The regularized
risk is non-smooth; The distance between the estimator and the true parameters vector cannot be
neglected. As a consequence, standard perturbative arguments that are the
traditional basis for asymptotic normality fail.
On the other hand, the Lasso estimator can be precisely characterized in the
regime in which both and are large, while is of order one. This
characterization was first obtained in the case of standard Gaussian designs,
and subsequently generalized to other high-dimensional estimation procedures.
Here we extend the same characterization to Gaussian correlated designs with
non-singular covariance structure. This characterization is expressed in terms
of a simpler ``fixed design'' model. We establish non-asymptotic bounds on the
distance between distributions of various quantities in the two models, which
hold uniformly over signals in a suitable sparsity class,
and values of the regularization parameter.
As applications, we study the distribution of the debiased Lasso, and show
that a degrees-of-freedom correction is necessary for computing valid
confidence intervals
Through-The-Barrier Communications in Isolated Class-E Converters Embedding a Low-k Transformer
In a recent paper, a through-the-barrier communication technique suitable for isolated resonant converters has been proposed. The approach is capable of sending data bidirectionally at high speed (one bit for each converter clock period) without the need of any additional isolating device other than the transformer necessary for the power transfer, and has been demonstrated by means of a proof-of-concept low-frequency prototype. In this paper we review that work under the assumption of increasing the operating frequency by using a coreless transformer presenting low losses, but also a low coupling factor k. This allows to increase the efficiency of the converter to a very high value (92% in the proposed design working at 6.78 MHz), but the communication speed has to be reduced (one bit every four clock cycles)
The High Voltage Regulator Board for the BDX Experiment
In this note we describe the design and construction of SiPM High Voltage (HV) Regulator board for the BDX experiment. The board is used to provide bias voltage to the Silicon PhotoMultipliers (SiPMs) used in the BDX detector. It hosts four independent channels, each with a selectable output voltage in the range 37 V to 80 V: each channel is individually regulated by means of a variable resistor. In the note, after a brief introduction to the BDX experiment, we present the design of the board, discussing in particular the critical aspects that we identified during the circuit implementation phase. We also show the results obtained from the characterization of a first sample of 10 boards
Stereoselective Reaction of 2-Carboxythioesters-1,3-dithiane with Nitroalkenes: An Organocatalytic Strategy for the Asymmetric Addition of a Glyoxylate Anion Equivalent.
Under mild reaction conditions γ-nitro-β-aryl-α-keto esters with up to 92% ee were obtained, realizing a formal catalytic stereoselective conjugate addition of the glyoxylate anion synthon
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