1,721,070 research outputs found
Velocità del suono nei fluidi Speed of sound in fluids
No full textLa velocità del suono è una grandezza fisica determinata dalle proprietà – temperatura, pressione, composizione – e dallo stato di aggregazione del mezzo in cui la perturbazione acustica si propaga. La sua misura sperimentale permette quindi di ottenere una stima delle proprietà che caratterizzano tali stati in una varietà di condizioni e di scale dimensionali, da microscopiche a planetarie. Limitandosi al caso di mezzi fluidi omogenei, si descrivono una serie di applicazioni della misura della velocità del suono che hanno un interesse scientifico o pratico attuale. Per ognuna di esse la descrizione è accompagnata da una illustrazione essenziale dei principi teorici che ne costituiscono il fondamento.The speed of sound is a physical quantity determined by the properties – temperature, pressure, composition – and by the state of matter of the acoustic propagation medium. As a consequence, the experimental determination of the speed of sound may provide an estimate of these properties in a variety of physical conditions over a range of dimensional scales spanning from microscopic to planetary. Limiting the discussion to consider the case of homogenous fluids, a number of current applications of such measurements which have a scientific or practical interest is reviewed. The description of each application is supplemented by a succinct illustration of the underlying theoretical basis
A Low-Cost Instrument for the Accurate Measurement of Resonances in Microwave Cavities
No full textSince vector network analysis became available, it
demonstrated its accuracy and versatility in a variety of applications,
including the accurate measurement of resonances in
microwave cavities. Unfortunately, the high cost and bulkiness
of vector network analyzers (VNAs) set a limit to their applicability.
This paper presents and discusses the design and the
initial performance tests of a simplified instrument which may
represent a valid alternative to VNAs in those applications where
the high quality factors of a microwave resonator have to be determined
with comparable accuracy but at low cost, allowing field
portability and the embedment in a more complex measurement
system. Triggered by the recent development of quasi-spherical
microwave resonators and their successful utilization in gas
metrology, we choose the extremely precise measurement of their
eigenfrequencies as a suitable test bench to validate the specifications
and assess the performance of the proposed instrument
The Euramet Metrology Research Programme Project Implementing the New Kelvin (InK)
No full textThe kelvin, along with the ampere, kilogram, and the mole are likely to
be redefined in terms of fundamental constants, in line with Conférence Générale
des Poids et Mesures resolution 1 (2011), sometime before 2020. In advance of,
and to support, the redefinition, a mise en pratique of the definition of the kelvin
(MeP-K) is currently being prepared. The Euramet Metrology Research Programme
Implementing the newkelvin (InK) project will coordinate research activity in this field
with the objective of improving primary thermometry over the range from 0.0009K
to >3000K. Specifically, the project will aim to pursue the following three broad
objectives: (1) Support the development of primary thermometry techniques for the
realization and dissemination of thermodynamic temperatures, particularly at high
(>1300K) and low (<1K) temperatures. This is a major objective of InK because
primary thermometry methods at the extremes of temperature should, in principle,
have lower uncertainties than defined scales. (2) Determine low uncertainty values
of T − T90 in the temperature region where the defined scale is expected to continue
providing the lowest uncertainties. This will support the development of theMeP-K and
help in the construction of a reliable data set for any possible future temperature scale.
(3) Use different thermodynamic thermometry methods to re-determine T − T2000 and therefore hopefully understand the cause of the discrepancy in the background
data that constitutes the Provisional Low Temperature Scale of 2000 (PLTS-2000).
An overview of the InK project, activities, and intended outcomes is given in this paper
Un risonatore sferico per misure di velocità del suono nei gas
No full textVengono descritti i risultati ottenuti con un risonatore sferico progettato per la misura di precisione della velocità del suono nei gas. Allo scopo di definire le prestazioni del risonatore in termini di precisione ed accuratezza raggiungibili nella misura, sono state effettuate misure in argon (100500 kPa) a temperatura ambiente. Le frequenze di risonanza fN e le semilarghezze gN di cinque modi puramente radiali sono state misurate con una precisione nell’ordine di 10-7•fN . I dati così ottenuti sono stati confrontati con quelli previsti da un modello che tiene conto dei fenomeni dissipativi predominanti che interessano un campo acustico stazionario in una geometria sferica
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