6,130 research outputs found
Criteri tli calcolo per il rivestimento termico di ugelli soggetti ad un flusso di gas ad alta temperatura (propellenti ad elevato impulso specifico) per durate relativamente lunghe
Il presente lavoro lia lo scopo di fornire dei criteri praticidi progetto per il rivestimento termico di ugelli per razzi ad elevatedurate di combustione.Lo sviluppo die lia condotto alla formulazione di detti criteri lia richiestoin una prima fase lo studio della propagazione del flusso di caloreattraverso una parete doppia costituita da materiali differenti (isolante emetallo); tale studio si è concluso definendo gli elementi base che caratterizzanoil fenomeno.Successivamente si è svolta una ricerca numerica allo scopo di esplorareil campo di variabilità di tali parametri caratteristici in vista di applicaredeterminati materiali e per l'involucro metallico e per il rivestimento.Tale indagine è stata effettuata mediante calcoli eseguiti con il computatoredigitale IBM 1620.A questo punto si è proceduto alla soluzione numerica del problemain forma adimensionale, la soluzione è stata effettuata per un certo numerodei parametri caratteristici allo scopo di ricoprire, dando valori determinati,t u t to il campo di variabilità di questi.Queste diverse soluzioni sono state ricavate mediante calcolatriceanalogica (DONNER) simulando il fenomeno della propagazione del calore.Diagrammati questi risultati si è infine definito un criterio per ottenererapidamente, in base alle caratteristiche dei gas, dei materiali usati e deglispessori relativi, i parametri caratteristici per i quali il calcolo già è staff)eseguito
Photodissociation and photoionisation of atoms and molecules of astrophysical interest
A new collection of photodissociation and photoionisation cross sections for
102 atoms and molecules of astrochemical interest has been assembled, along
with a brief review of the basic processes involved. These have been used to
calculate dissociation and ionisation rates, with uncertainties, in a standard
ultraviolet interstellar radiation field (ISRF) and wavelength-dependent
radiation fields. The new ISRF rates generally agree within 30% with our
previous compilations, with a few notable exceptions. The reduction of rates in
shielded regions was calculated as a function of dust, molecular and atomic
hydrogen, atomic C, and self-shielding column densities. The relative
importance of shielding types depends on the species in question and the dust
optical properties. The new data are publicly available from the Leiden
photodissociation and ionisation database.
Sensitivity of rates to variation of temperature and isotope, and cross
section uncertainties, are tested. Tests were conducted with an
interstellar-cloud chemical model, and find general agreement (within a factor
of two) with the previous iteration of the Leiden database for the ISRF, and
order-of-magnitude variations assuming various kinds of stellar radiation. The
newly parameterised dust-shielding factors makes a factor-of-two difference to
many atomic and molecular abundances relative to parameters currently in the
UDfA and KIDA astrochemical reaction databases. The newly-calculated cosmic-ray
induced photodissociation and ionisation rates differ from current standard
values up to a factor of 5. Under high temperature and cosmic-ray-flux
conditions the new rates alter the equilibrium abundances of abundant dark
cloud abundances by up to a factor of two. The partial cross sections for H2O
and NH3 photodissociation forming OH, O, NH2 and NH are also evaluated and lead
to radiation-field-dependent branching ratios.Comment: Corrected some inconsistent table/figure data. Significant change: Zn
photoionisation rate corrected. Accepted for publication by A&
Molecular pathology of colorectal cancer.
Colorectal cancer (CRC) is one of the most intensively studied cancer types, partly because of its high prevalence but also because of the existence of its precursor lesions, tubular or villous adenomas, and more recently (sessile) serrated adenomas, which can be detected endoscopically and removed. The morphological steps in the adenoma-carcinoma sequence have been elucidated at a molecular level, which has been facilitated by identification of the genes responsible for familial intestinal cancer. However, apart from early detection of familial forms of CRC and its use in genetic counseling, until recently such detailed molecular knowledge has had little impact on clinical management of the disease. This has dramatically changed in the last decade. With drugs specifically targeting the epidermal growth factor receptor (EGFR) having been shown effective in CRC, mechanisms responsible for resistance have been explored. The finding that KRAS mutated cancers do not respond to anti-EGFR treatment has had a profound impact on clinical management and on molecular diagnostics of CRC. Additional genetic tests for mutations in NRAS, BRAF and PIK3CA contribute to determining who to treat, and others will follow. New therapies effective in patients with advanced CRC are under investigation. Remaining burning questions for optimal management are which patients will relapse after resection of the primary tumor and which patients will respond to the standard 5FU-oxaliplatin adjuvant treatment regimen. Predictive tests to address these issues are eagerly awaited. New classifications of CRC, based on molecular parameters, are emerging, and we will be confronted with new subtypes of CRC, for which the definition is based on combinations of gene expression patterns, chromosomal alterations, gene mutations and epigenetic characteristics. This will be instrumental in designing new approaches for therapy but will also be translated into molecular diagnostics. Both will contribute to improved clinical management of CRC
Efficiency of radial transport of ices in protoplanetary disks probed with infrared observations: the case of CO
The efficiency of radial transport of icy solid material from outer disk to
the inner disk is currently unconstrained. Efficient radial transport of icy
dust grains could significantly alter the composition of the gas in the inner
disk. Our aim is to model the gaseous CO abundance in the inner disk and
use this to probe the efficiency of icy dust transport in a viscous disk.
Features in the simulated CO spectra are investigated for their dust flux
tracing potential. We have developed a 1D viscous disk model that includes gas
and grain motions as well as dust growth, sublimation and freeze-out and a
parametrisation of the CO chemistry. The thermo-chemical code DALI was used
to model the mid-infrared spectrum of CO, as can be observed with
JWST-MIRI. CO ice sublimating at the iceline increases the gaseous CO
abundance to levels equal to the CO ice abundance of , which
is three orders of magnitude more than the gaseous CO abundances of observed by Spitzer. Grain growth and radial drift further increase
the gaseous CO abundance. A CO destruction rate of at least
s is needed to reconcile model prediction with observations. This rate
is at least two orders of magnitude higher than the fastest known chemical
destruction rate. A range of potential physical mechanisms to explain the low
observed CO abundances are discussed. Transport processes in disks can have
profound effects on the abundances of species in the inner disk. The
discrepancy between our model and observations either suggests frequent shocks
in the inner 10 AU that destroy CO, or that the abundant midplane CO is
hidden from our view by an optically thick column of low abundance CO in to
the disk surface XDR/PDR. Other molecules, such as CH or NH, can give
further handles on the rate of mass transport.Comment: Accepted for publication in A&A, 18 pages, 13 figures, abstract
abridge
The first ultra-high resolution Digital Terrain Model of the shallow-water sector around Lipari Island (Aeolian Islands, Italy)
Very high resolution bathymetric map obtained through multibeam echosounders
data are crucial to generate accurate Digital Terrain Models
from which the morphological setting of active volcanic areas can be analyzed
in detail. Here we show and discuss the main results from the first
multibeam bathymetric survey performed in shallow-waters around the island
of Lipari, the largest and the most densely populated of the Aeolian
Islands (southern Italy). Data have been collected in the depth range of
0.1-150 m and complete the already existent high-resolution multibeam
bathymetry realized between 100 and 1300 m water depth. The new ultrahigh
resolution bathymetric maps at 0.1-0.5 m provide new insights on the
shallow seafloor of Lipari, allowing to detail a large spectrum of volcanic,
erosive-depositional and anthropic features. Moreover, the presented data
allow outlining the recent morphological evolution of the shallow coastal
sector of this active volcanic island, indicating the presence of potential
geo-hazard factors in shallow waters
Multi-mode ultra-strong coupling in circuit quantum electrodynamics
With the introduction of superconducting circuits into the field of quantum
optics, many novel experimental demonstrations of the quantum physics of an
artificial atom coupled to a single-mode light field have been realized.
Engineering such quantum systems offers the opportunity to explore extreme
regimes of light-matter interaction that are inaccessible with natural systems.
For instance the coupling strength can be increased until it is comparable
with the atomic or mode frequency and the atom can be coupled to
multiple modes which has always challenged our understanding of light-matter
interaction. Here, we experimentally realize the first Transmon qubit in the
ultra-strong coupling regime, reaching coupling ratios of
and we measure multi-mode interactions through a hybridization of the qubit up
to the fifth mode of the resonator. This is enabled by a qubit with 88% of its
capacitance formed by a vacuum-gap capacitance with the center conductor of a
coplanar waveguide resonator. In addition to potential applications in quantum
information technologies due to its small size and localization of electric
fields in vacuum, this new architecture offers the potential to further explore
the novel regime of multi-mode ultra-strong coupling.Comment: 15 pages, 9 figure
Reionization history constraints from neural network based predictions of high-redshift quasar continua
Observations of the early Universe suggest that reionization was complete by
, however, the exact history of this process is still unknown. One
method for measuring the evolution of the neutral fraction throughout this
epoch is via observing the Ly damping wings of high-redshift quasars.
In order to constrain the neutral fraction from quasar observations, one needs
an accurate model of the quasar spectrum around Ly, after the spectrum
has been processed by its host galaxy but before it is altered by absorption
and damping in the intervening IGM. In this paper, we present a novel machine
learning approach, using artificial neural networks, to reconstruct quasar
continua around Ly. Our QSANNdRA algorithm improves the error in this
reconstruction compared to the state-of-the-art PCA-based model in the
literature by 14.2% on average, and provides an improvement of 6.1% on average
when compared to an extension thereof. In comparison with the extended PCA
model, QSANNdRA further achieves an improvement of 22.1% and 16.8% when
evaluated on low-redshift quasars most similar to the two high-redshift quasars
under consideration, ULAS J1120+0641 at and ULAS J1342+0928 at
, respectively. Using our more accurate reconstructions of these two
quasars, we estimate the neutral fraction of the IGM using a homogeneous
reionization model and find at
and at . Our
results are consistent with the literature and favour a rapid end to
reionization
Approaching ultra-strong coupling in Transmon circuit-QED using a high-impedance resonator
In this experiment, we couple a superconducting Transmon qubit to a
high-impedance microwave resonator. Doing so leads to a large
qubit-resonator coupling rate , measured through a large vacuum Rabi
splitting of MHz. The coupling is a significant fraction of the
qubit and resonator oscillation frequencies , placing our system close
to the ultra-strong coupling regime ( on resonance).
Combining this setup with a vacuum-gap Transmon architecture shows the
potential of reaching deep into the ultra-strong coupling
with Transmon qubits
The significance of indirect costs—application to clinical laboratory test economics using computer facilities
The significance of indirect costs in the cost price calculation of
clinical chemistry laboratory tests by way of the production centres
method has been investigated. A cost structure model based on the ‘production centres’ method, the Academisch Ziekenhuis Groningen
(AZG) 1-2-3 model, is used for the calculation of cost and cost
prices as an add-in tool to the spreadsheet program Lotus 1-2-3.
The system specifications of the AZG 1-2-3 cost structure model
have been extended with facilities to impute all relevant indirect
costs to cost centres by aid of allocation rules, which can be chosen
freely. The inference is made that as indirect costs play a more
important part in decision-making processes concerning planning
and control, the specification of the relation to the cost centres
should be determined in a more detailed way. The AZG 1-2-3 cost
structure model has therefore been extended in order to increase the
significance as a management tool for laboratory management
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