5,858 research outputs found
A genetic algorithm-assisted semi-adaptive MMSE multi-user detection for MC-CDMA mobile communication systems
In this work, a novel Minimum-Mean Squared-Error (MMSE) multi-user detector is proposed for MC-CDMA transmission systems working over mobile radio channels characterized by time-varying multipath fading. The proposed MUD algorithm is based on a Genetic Algorithm (GA)-assisted per-carrier MMSE criterion. The GA block works in two successive steps: a training-aided step aimed at computing the optimal receiver weights using a very short training sequence, and a decision-directed step aimed at dynamically updating the weights vector during a channel coherence period. Numerical results evidenced BER performances almost coincident with ones yielded by ideal MMSE-MUD based on the perfect knowledge of channel impulse response. The proposed GA-assisted MMSE-MUD clearly outperforms state-of-the-art adaptive MMSE receivers based on deterministic gradient algorithms, especially for high number of transmitting users
Photometric and proper motion study of neglected open cluster NGC 2215
Optical UBVRI photometric measurements using the Faulkes Telescope North were
taken in early 2011 and combined with 2MASS JHK and WISE infrared
photometry as well as UCAC4 proper motion data in order to estimate the main
parameters of the galactic open cluster NGC 2215 of which large uncertainty
exists in the current literature. Fitting a King model we estimate a core
radius of 1.120.04 (0.240.01pc) and a limiting radius of
0.5 (0.940.11pc) for the cluster. The results of isochrone
fits indicates an age of with a distance of
pc, a metallicity of dex and a reddening of
. A proportion of the work in this study was undertaken by
Australian and Canadian upper secondary school students involved in the Space
to Grow astronomy education project, and is the first scientific publication to
have utilized our star cluster photometry curriculum materials.Comment: 10 pages, 9 Figures, 3 Table
Minimum error discrimination of Pauli channels
We solve the problem of discriminating with minimum error probability two
given Pauli channels. We show that, differently from the case of discrimination
between unitary transformations, the use of entanglement with an ancillary
system can strictly improve the discrimination, and any maximally entangled
state allows to achieve the optimal discrimination. We also provide a simple
necessary and sufficient condition in terms of the structure of the channels
for which the ultimate minimum error probability can be achieved without
entanglement assistance. When such a condition is satisfied, the optimal input
state is simply an eigenstate of one of the Pauli matrices.Comment: 8 pages, no figure
The submerged structure and stratal architecture of the Neapolitan Yellow Tuff (NYT) caldera, offshore the Campi Flegrei, (Eastern Tyrrhenian Margin): new insights from high resolution seismics and gravity core data
The Campi Flegrei is an active volcanic area defined by a
quasi-circular depression that covers some 200 km2 of the coastal
zone of SW Italy, a large part of which develops off the Naples
(Pozzuoli) Bay (Fig. 1). The area has been active at least since 60
ka BP ( Pappalardo et al., 1999), and is structurally dominated by a
caldera, 6 km in diameter, associated with the eruption of the
Neapolitan Yellow Tuff (NYT), a 40 km3 Dense Rock Equivalent
(DRE) ignimbrite (Scarpati et al., 1993) dated at ca 15 ka BP
(Deino et al., 2004), that covered the district now occupied by the
city of Naples, the Campi Flegrei and a large area of the
continental shelf off the Pozzuoli Bay.
The volcanological evolution of the NYT caldera as been long
described on the basis of outcrop and subsurface studies onland
(Rosi & Sbrana, 1987; Orsi et al., 1996, 2004 and references
therein; Di Vito et al., 1999; Perrotta et al., 2006; Fedele et al.,
2011), but its offshore morphology, detailed structure and recent
stratigraphic setting are still poorly understood.
In this study we integrate geological and geophysical data of
different resolution/penetration obtained from high-resolution
reflection seismic profiles (Sparker and Chirp source) with gravity
core and swath bathymetry to better constrain the shallow
structure, stratigraphic architecture and latest Quaternary to
Holocene evolution of the submerged sector of the NYT caldera
off the Pozzuoli Bay.
Our data clearly image, for the first time, the offshore geometry
of the NYT caldera ring-fault zone, as well as the style and timing
of volcano-tectonic deformation associated with the late stage
evolution of the NYT inner caldera resurgence. Our interpretation
suggests that since 15 ka the offshore sector of NYT inner caldera
underwent significant deformation and uplift (with minor
subsidence episodes) that occurred at almost the same rate as the
post-glacial sea-level rise. Particularly, the inner Pozzuoli Bay
started to deform soon after 15 ka BP, when sea-level rise was
initially faster than uplift. This caused a general increase of the
accommodation space that was progressively filled up by
volcaniclastic sediments. Since ca. 8 ka BP, along with the mid
Holocene decrease in the rate of the sea-level rise, the early NYT
resurgent structure was then uplifted up to the sea-level or even to
partial subaerial exposure. From ca. 8 to 5 ka BP two distinct
layers of volcaniclastic resediments, mostly represented by gravity
flow deposits, formed throughout the Bay. A significant post-
Roman (post 2 ka BP) subsidence phase of ca 10 m is then
recorded offshore Pozzuoli by the drowning of the infralittoral
prograding wedge below the present-day fair-weather wave base.
REFERENCES
Deino AL, Orsi G, de Vita S, Piochi M (2004) The age of the Neapolitan Yellow
Tuff caldera-forming eruption (Campi Flegrei caldera—Italy) assessed by
40Ar/39Ar dating method. J. Volcanol. Geotherm. Res. 133, 157–170.
Di Vito M., Isaia R., Orsi G., Southon J., de Vita S., D’Antonio M., Pappalardo
L., Piochi M., 1999. Volcanism and deformation since 12,000 years at the
Campi Flegrei caldera (Italy), J. Volcanol. Geotherm. Res. 91 (2-4), 221-246.
Fedele L., Insinga D.D., Calvert A.T., Morra V., Perrotta A., Scarpati C., 2011.
40Ar/39Ar dating of tuff vents in the Campi Flegrei caldera (southern Italy):
toward a new chronostratigraphic reconstruction of the Holocene volcanic
activity. Bull. Volcanol. 73, 1323-1336.
Orsi G, de Vita S, Di Vito M, 1996. The restless, resurgent Campi Flegrei nested
caldera (Italy): constraints on its evolution and configuration. J. Volcanol.
Geotherm. Res. 74, 179–214.
Orsi G., Di Vito M.A. Isaia R., 2004. Volcanic hazard assessment at the restless
Campi Flegrei caldera. Bull. Volcanol. 66, 514–530.
Pappalardo L., Civetta L., D’Antonio M., Deino A., Di Vito M., Orsi G.,
Carandente A., de Vita S., Isaia R. & Piochi M., 1999. Chemical and Srisotopical
evolution of the Phlegrean magmatic system before the Campanian
Ignimbrite and the Neapolitan Yellow Tuff eruptions J. Volcanol. Geotherm.
Res. 91, 141-166.
Perrotta A., Scarpati C., Luongo G., Morra V., 2006. The Campi Flegrei caldera
boundary in the city of Naples. In: De Vivo B (ed) Volcanism in the
Campania Plain: Vesuvius, Campi Flegrei and Ignimbrites. Elsevier,
Amsterdam, pp 85–96 (in the series Developments in Volcanology, 9)
Scarpati C., Cole P., & Perrotta A., 1993. The Neapolitan Yellow Tuff- A large
volume multiphase eruption from Campi Flegrei, Southern Italy. Bull.
Volcan. 55, 343-35
Architettura stratigrafica ed evoluzione del Golfo di Pozzuoli negli ultimi 15 ka:una nuova prospettiva sulla caldera del Tufo Giallo Napoletano,Campi Flegrei, margine tirrenico orientale.
I Campi Flegrei rappresentano un distretto vulcanico attivo che si sviluppa al confine tra il settore emerso
e sommerso del margine continentale campano. Il distretto vulcanico occupa una superficie di circa 200 km2,
è strutturalmente dominato da una caldera di collasso del diametro di circa 8 km formatasi in seguito
all’eruzione del Tufo Giallo Napoletano (TGN), un deposito ignimbritico del volume di 30-50 km3 Dense
Rock Equivalent, datato a 15 ka B.P. circa, ed è attivo da almeno 78 ka B.P circa.
L’obiettivo di questo lavoro è di ricostruire l’architettura stratigrafica e l’evoluzione vulcanotettonica
tardo-Quaternaria del sistema caldera di collasso - faglia anulare - risorgenza intra-calderica del settore
sommerso della caldera del TGN. A tal fine è stata analizzata una fitta maglia di profili sismici a riflessione
monocanale di alta (Sparker) ed altissima (Subbottom Chirp) risoluzione. I dati sismici sono stati
successivamente integrati sia con quelli ottenuti dall’analisi di carotaggi a gravità e batimetrici multibeam
che con quelli disponibili in letteratura e, nell’insieme, analizzati in ambiente GIS.
I nuovi dati indicano che il settore interno dell’area collassata a seguito dell’eruzione del TGN evolve
inizialmente in condizioni di mare basso. L’area intra-calderica viene successivamente interessata dalla
formazione di una struttura antiforme (risorgenza intra-calderica) il cui tasso di sollevamento è stato
comparabile con l’innalzamento eustatico nell’intervallo Pleistocene superiore – Olocene [Lambeck et al.,
2011]. A circa 10 ka B.P. il settore centrale della struttura risorgente raggiunge l’esposizione subaerea
(terrazzo morfologico de “La Starza”).
La calibrazione dei profili sismici Chirp con markers tefro-stratigrafici riconosciuti in un carotaggio e
datati al 1538 A.D., 79 A.D. indica l’instaurarsi di un periodo di subsidenza in epoca post-Romana, registrato
dall’annegamento di 10-25 m del cuneo di progradazione infralittorale rispetto alle profondità di equilibrio
funzionale attualmente segnalate in area Mediterranea. L’interpretazione sismostratigrafica rivela, inoltre, la
presenza di fluidi che risalgono attraverso la zona di faglia anulare che delimita la caldera del TGN.
Bibliografia
Lambeck, K., Antonioli, F., Anzidei, M., Ferranti, L., Leoni, G., Scicchitano, G., Silenzi, S., (2011). Sea
level change along the Italian coast during the holocene and projections for the future. Quaternary
International, 232, 250-257
Seismic expression of the shallow structure of The Neapolitan Yellow Tuff (NYT) caldera offshore the Campi Flegrei
In this study we integrate high-resolution swath bathymetry, single-channel reflection seismic data and gravity core
data, to provide new insights into the shallow structure and latest Quaternary to Holocene evolution of the submerged
sector of the Neapolitan Yellow Tuff (NYT) caldera (Campi Flegrei) in the Pozzuoli Bay. The new data allow for a
reconstruction of the offshore geometry of the NYT caldera collapse \u2013 ring fault system, along with the style and timing
of deformation of the inner caldera resurgence.
Our interpretation shows that the NYT eruption (~15 ka BP) was associated with a caldera collapse bounded by an
inward-dipping ring fault system. The ring fault system consists in a 1-2 km wide fault zone that encircles an inner
caldera region ~ 5 km in diameter and is often marked by the occurrence of pore fluids ascending through the fault
zone, up to the seafloor, particularly in the western sector of the bay. A shallow magmatic intrusion along the ring fault
zone was also detected offshore Bagnoli in the eastern part of the Pozzuoli Bay (Sacchi et al., 2014).
Following the NYT eruption, the inner caldera region underwent significant deformation and resurgence with a
maximum cumulative uplift of the offshore structure in the order of 180 m. The net uplift rate of the caldera resurgent
dome was ~ 9 - 12 mm/year during the period 15.0 \u2013 6.6 ka BP. The style of deformation of the resurgent structure can
be described in terms of a broad doming, accompanied by subordinate brittle deformation, mostly concentrated in a
small apical graben at the summit of the resurgent dome (Cole et al., 2005).
Chronostratigraphic calibration of seismic profiles obtained by three tephra layers cored in the Pozzuoli Bay
indicates 5 to 25 m of post-Roman differential subsidence and tilting towards ESE of the inner caldera resurgence, as
recorded by the drowning of the infralittoral prograding wedge below the present-day storm wave base
HST resolves stars in a tiny body falling on the dwarf galaxy DDO 68
We present new Hubble Space Telescope (HST) imaging of a stream-like system
associated with the dwarf galaxy DDO 68, located in the Lynx-Cancer Void at a
distance of D12.65 Mpc from us. The stream, previously identified in deep
Large Binocular Telescope images as a diffuse low surface brightness structure,
is resolved into individual stars in the F606W (broad V) and F814W (I)
images acquired with the Wide Field Camera 3. The resulting V, I
color-magnitude diagram (CMD) of the resolved stars is dominated by old
(age1-2 Gyr) red giant branch (RGB) stars. From the observed RGB tip,
we conclude that the stream is at the same distance as DDO 68, confirming the
physical association with it. A synthetic CMD analysis indicates that the large
majority of the star formation activity in the stream occurred at epochs
earlier than 1 Gyr ago, and that the star formation at epochs more recent
than 500 Myr ago is compatible with zero. The total stellar mass of the
stream is , about 1/100 of that of DDO~68. This is a
striking example of hierarchical merging in action at the dwarf galaxy scales.Comment: ApJ in pres
Informationally complete measurements and groups representation
Informationally complete measurements on a quantum system allow to estimate
the expectation value of any arbitrary operator by just averaging functions of
the experimental outcomes. We show that such kind of measurements can be
achieved through positive-operator valued measures (POVM's) related to unitary
irreducible representations of a group on the Hilbert space of the system. With
the help of frame theory we provide a constructive way to evaluate the
data-processing function for arbitrary operators.Comment: 9 pages, no figures, IOP style. Some new references adde
Chemical abundances and radial velocities in the extremely metal-poor galaxy DDO 68
We present chemical abundances and radial velocities of six HII regions in
the extremely metal-poor star-forming dwarf galaxy DDO 68. They are derived
from deep spectra in the wavelength range 3500 - 10,000 {\AA}, acquired with
the Multi Object Double Spectrograph (MODS) at the Large Binocular Telescope
(LBT). In the three regions where the [O III]4363 {\AA} line was
detected, we inferred the abundance of He, N, O, Ne, Ar, and S through the
"direct" method. We also derived the oxygen abundances of all the six regions
adopting indirect method calibrations. We confirm that DDO 68 is an extremely
metal-poor galaxy, and a strong outlier in the luminosity - metallicity
relation defined by star-forming galaxies. With the direct-method we find
indeed an oxygen abundance of 12+log(O/H)=7.140.07 in the northernmost
region of the galaxy and, although with large uncertainties, an even lower
12+log(O/H)=6.960.09 in the "tail". This is, at face value, the most
metal-poor direct abundance detection of any galaxy known. We derive a radial
oxygen gradient of -0.060.03 dex/kpc (or -0.30 dex ) with the
direct method, and a steeper gradient of -0.120.03 dex/kpc (or -0.59 dex
) from the indirect method. For the -element to oxygen
ratios we obtain values in agreement with those found in other metal-poor
star-forming dwarfs. For nitrogen, instead, we infer much higher values,
leading to log(N/O), at variance with the suggested existence of a
tight plateau at in extremely metal poor dwarfs. The derived helium mass
fraction ranges from Y=0.2400.005 to Y=0.250.02, compatible with
standard big bang nucleosynthesis. Finally, we measured HII region radial
velocities in the range 479522 km/s from the tail to the head of the
"comet", consistent with the rotation derived in the HI.Comment: Accepted for publication in MNRA
Superbroadcasting of continuous variables mixed states
We consider the problem of broadcasting quantum information encoded in the
average value of the field from N to M>N copies of mixed states of radiation
modes. We derive the broadcasting map that preserves the complex amplitude,
while optimally reducing the noise in conjugate quadratures. We find that from
two input copies broadcasting is feasible, with the possibility of simultaneous
purification (superbroadcasting). We prove similar results for purification
(M<=N) and for phase-conjugate broadcasting.Comment: 11 pages, 1 figure, revtex4 style, revised versio
- …