1,477 research outputs found
Analyses for equivalent ratio model in measurements of high standard resistance bridges
Presso l'Istituto Nazionale di Ricerca Metrologica (INRiM) è stata effettuata una prima valutazione esplorativa di un modello a rapporto equivalente per un ponte commerciale a doppia sorgente utilizzando regole di triangolazione metrologica restrittive. Lo studio è stato condotto osservando le misure di rapporto di resistenze campione nel campo da 10 Tohm a 1 Pohm.At the National Institute of Metrological Research (INRiM), a first evaluation of an exploratory method in the equivalent ratio model for a commercial dual source, high resistance bridge has been made using restrictive metrological triangulation rules. The study was performed observing the ratios measurements of a commercial bridge for the standard resistors in the range from 10 Tohm to 1 Pohm
Statistical tools for analysis of the performance of a high resistance measurement bridge
Il rapporto tecnico descrive l’utilizzo delle varianze di Allan e della densità di potenza spettrale per individuare le sorgenti di rumore che si possono riscontrare nel funzionamento del ponte di
Wheatstone modificato di alta resistenza di tipo commerciale. Lo studio è stato condotto osservando le misure di corrente del detector del ponte in funzione del tempo di integrazione del medesimo. Da
un’analisi preliminare dei dati ottenuti sono stati individuate le principali sorgenti di rumore del sistema in corrispondenza dei tempi di integrazione del detectorThe technical report exploits the use of Allan variances and the spectral power density to analyze the performance of the high resistance measurement Wheatstone modified bridge of commercial type.
The study was performed by observing the current measurements of the bridge detector as a function of its integration time. From a preliminary analysis of the data obtained, the main sources of noise of
the system have been identified in correspondence with the integration times of the detector
A Statistical Analysis of Multipath Interference for Impulse Radio UWB Systems
In this paper, we develop a statistical characterization of the multipath
interference in an Impulse Radio (IR)-UWB system, considering the standardized
IEEE 802.15.4a channel model. In such systems, the chip length has to be
carefully tuned as all the propagation paths located beyond this limit can
cause interframe/intersymbol interferences (IFI/ISI). Our approach aims at
computing the probability density function (PDF) of the power of all multipath
components with delays larger than the chip time, so as to prevent such
interferences. Exact analytical expressions are derived first for the
probability that the chip length falls into a particular cluster of the
multipath propagation model and for the statistics of the number of paths
spread over several contiguous clusters. A power delay profile (PDP)
approximation is then used to evaluate the total interference power as the
problem appears to be mathematically intractable. Using the proposed
closed-form expressions, and assuming minimal prior information on the channel
state, a rapid update of the chip time value is enabled so as to control the
signal to interference plus noise ratio.Comment: 17 pages, 9 figures; submitted to the Journal of the Franklin
Institute on Sept. 24, 201
Measurement Method for Evaluating the Probability Distribution of the Quality Factor of Mode-Stirred Reverberation Chambers
An original experimental method for determining the empirical probability
distribution function (PDF) of the quality factor (Q) of a mode-stirred
reverberation chamber is presented. Spectral averaging of S-parameters across a
relatively narrow frequency interval at a single pair of locations for the
transmitting and receiving antennas is applied to estimate the stored and
dissipated energy in the cavity, avoiding the need for spatial scanning to
obtain spatial volume or surface averages. The effective number of
simultaneously excited cavity modes per stir state, M, can be estimated by
fitting the empirical distribution to the parametrized theoretical
distribution. The measured results support a previously developed theoretical
model for the PDF of Q and show that spectral averaging over a bandwidth as
small as a few hundred kHz is sufficient to obtain accurate results.Comment: submitted for publicatio
Fast hashing with Strong Concentration Bounds
Previous work on tabulation hashing by Patrascu and Thorup from STOC'11 on
simple tabulation and from SODA'13 on twisted tabulation offered Chernoff-style
concentration bounds on hash based sums, e.g., the number of balls/keys hashing
to a given bin, but under some quite severe restrictions on the expected values
of these sums. The basic idea in tabulation hashing is to view a key as
consisting of characters, e.g., a 64-bit key as characters of
8-bits. The character domain should be small enough that character
tables of size fit in fast cache. The schemes then use tables
of this size, so the space of tabulation hashing is . However, the
concentration bounds by Patrascu and Thorup only apply if the expected sums are
.
To see the problem, consider the very simple case where we use tabulation
hashing to throw balls into bins and want to analyse the number of
balls in a given bin. With their concentration bounds, we are fine if ,
for then the expected value is . However, if , as when tossing
unbiased coins, the expected value is for large data sets,
e.g., data sets that do not fit in fast cache.
To handle expectations that go beyond the limits of our small space, we need
a much more advanced analysis of simple tabulation, plus a new tabulation
technique that we call \emph{tabulation-permutation} hashing which is at most
twice as slow as simple tabulation. No other hashing scheme of comparable speed
offers similar Chernoff-style concentration bounds.Comment: 54 pages, 3 figures. An extended abstract appeared at the 52nd Annual
ACM Symposium on Theory of Computing (STOC20
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