278 research outputs found
A convergent decomposition algorithm for support vector machines.
In this work we consider nonlinear minimization problems with a single linear equality constraint and box constraints. In particular we are interested in solving problems where the number of variables is so huge that traditional optimization methods cannot be directly applied. Many interesting real world problems lead to the solution of large scale constrained problems with this structure. For example, the special subclass of problems with convex quadratic objective function plays a fundamental role in the training of Support Vector Machine, which is a technique for machine learning problems. For this particular subclass of convex quadratic problem, some convergent decomposition methods, based on the solution of a sequence of smaller subproblems, have been proposed. In this paper we define a new globally convergent decomposition algorithm that differs from the previous methods in the rule for the choice of the subproblem variables and in the presence of a proximal point modification in the objective function of the subproblems. In particular, the new rule for sequentially selecting the subproblems appears to be suited to tackle large scale problems, while the introduction of the proximal point term allows us to ensure the global convergence of the algorithm for the general case of nonconvex objective function. Furthermore, we report some preliminary numerical results on support vector classification problems with up to 100 thousands variables
Machine Learning for the prediction of the dynamic behavior of a small scale ORC system
This work was funded by the 2016 Scholarship of the Knowledge Center on OrganicRankine Cycle (KC ORC, www.kcorc.org), awarded to Lorenzo Tocci to work on this researchproject with Dr Pesyridis at Brunel University London. Entropea Labs is also acknowledgedfor the economic and technical support provided during the completion of this study.2016 Scholarship of the Knowledge Center on Organic Rankine Cycle (KC ORC, www.kcorc.org
A project for polarimetric observations in single dish with Medicina and Noto 32 m antennas
A project with multidisciplinary characteristics, aimed to implement the possibility of polarimetric measurements in single dish at the VLBI stations of Medicina and Noto, is presented. The project will open a new window on many
astrophysical items that may be approached using the already existing instrumentation and facilities of the two Italian radioastronomical stations. We report here some scientific backgrounds, together with some technical evaluations, on which the feasibility of the project is based
Trigonometric Parallaxes of Massive Star Forming Regions: IV. G35.20-0.74 and G35.20-1.74
We report trigonometric parallaxes for the high-mass star forming regions
G35.20-0.74 and G35.20-1.74, corresponding to distances of 2.19 (+0.24 -0.20)
kpc and 3.27 (+0.56 -0.42) kpc, respectively. The distances to both sources are
close to their near kinematic distances and place them in the
Carina-Sagittarius spiral arm. Combining the distances and proper motions with
observed radial velocities gives the locations and full space motions of the
star forming regions. Assuming a standard model of the Galaxy, G35.20-0.74 and
G35.20-1.74 have peculiar motions of ~13 km/s and ~16 km/s counter to Galactic
rotation and ~9 km/s toward the North Galactic Pole.Comment: 16 pages, 8 figure
Water maser variability over 20 years in a large sample of star-forming regions: the complete database
Context. Water vapor emission at 22 GHz from masers associated with
star-forming regions is highly variable. Aims. We present a database of up to
20 years of monitoring of a sample of 43 masers within star-forming regions.
The sample covers a large range of luminosities of the associated IRAS source
and is representative of the entire population of H2O masers of this type. The
database forms a good starting point for any further study of H2O maser
variability. Methods. The observations were obtained with the Medicina 32-m
radiotelescope, at a rate of 4-5 observations per year. Results. To provide a
database that can be easily accessed through the web, we give for each source:
plots of the calibrated spectra, the velocity-time-flux density plot, the light
curve of the integrated flux, the lower and upper envelopes of the maser
emission, the mean spectrum, and the rate of the maser occurrence as a function
of velocity. Figures for just one source are given in the text for
representative purposes. Figures for all the sources are given in electronic
form in the on-line appendix. A discussion of the main properties of the H2O
variability in our sample will be presented in a forthcoming paper.Comment: 11 pages, 9 figures, to be published in Astronomy and Astrophysics;
all plots in appendix (not included) can be downloaded from
http://www.arcetri.astro.it/~starform/water_maser_v2.html or
http://www.ira.inaf.it/papers/masers/water_maser_v2.htm
Evidence that a salt bridge in the light chain contributes to the physical stability difference between heavy and light human ferritins.
Human ferritin, a multimeric iron storage protein, is composed by various proportions of two subunit types: the H- and L-chains. The biological functions of these two genic products have not been clarified, although differences in reactivity with iron have been shown. Starting from the hypothesis that the high stability typical of ferritin is an important property which may be relevant for its iron storage function, we studied ferritin homopolymers of H- and L-chains in different denaturing conditions. In addition we analyzed 13 H-chain variants with alterations in regions conserved within mammalian H-chains. In all the denaturation experiments H-chain ferritin showed lower stability than L-chain ferritin. The difference was greater in guanidine HCl denaturation experiments, where the end products are fully unfolded peptides, than in acidic denaturation experiments, where the end products are peptides with properties analogous to "molten globule." The study on H-chain variants showed: (i) ferritin stability was not affected by alterations of regions exposed to the inner or outer surface of the shell and not involved in intra- or inter-chain interactions; (ii) stability was reduced by alterations of sequences involved in inter-subunit interactions such as the deletion of the N-terminal extension or substitutions along the hydrophobic and hydrophilic channels; (iii) stability was increased by the substitution of 2 amino acids inside the four-helix bundle with those of the homologous L-chain. One of the residues is involved in a salt bridge in the L-chain, and we concluded that the stability difference between H- and L-ferritins is to a large extent due to the stabilizing effect of this salt bridge on the L-subunit fold
Hard X-ray emission in the star-forming region ON2: discovery with XMM-Newton
We obtained X-ray XMM-Newton observations of the open cluster Berkeley 87 and
the massive star-forming region (SFR) ON 2. In addition, archival infrared
Spitzer Space Telescope observations were used. It is likely that the SFR ON 2
and Berkeley 87 are at the same distance, 1.23 kpc, and hence are associated.
The XMM-Newton observations detected X-rays from massive stars in Berkeley 87
as well as diffuse emission from the SFR ON 2. The two patches of diffuse X-ray
emission are encompassed in the shell-like H II region GAL 75.84+0.40 in the
northern part of ON 2 and in the ON 2S region in the southern part of ON 2. The
diffuse emission from GAL 75.84+0.40 suffers an absorption column equivalent to
A_V approx. 28 mag. Its spectrum can be fitted either with a thermal plasma
model at T < 30 MK or by an absorbed power-law model with gamma; approx. -2.6.
The X-ray luminosity of GAL 75.84+0.40 is L_X approx. 6 10^31 erg/s. The
diffuse emission from ON 2S is adjacent to the ultra-compact H II (UCHII)
region Cygnus 2N, but does not coincide with it or with any other known UCHII
region. It has a luminosity of L_X approx. 4 10^31 erg/s. The spectrum can be
fitted with an absorbed power-law model with gamma; approx.-1.4. We adopt the
view of Turner and Forbes (1982) that the SFR ON 2 is physically associated
with the massive star cluster Berkeley 87 hosting the WO type star WR 142. We
discuss different explanations for the apparently diffuse X-ray emission in
these SFRs. These include synchrotron radiation, invoked by the co-existence of
strongly shocked stellar winds and turbulent magnetic fields in the
star-forming complex, cluster wind emission, or an unresolved population of
discrete sources.Comment: ApJ 2010, 712, 763. Reduced fig. resolution. Full resolution version
is at
http://www.astro.physik.uni-potsdam.de/research/abstracts/oskinova-ber87.htm
Supersonic water masers in 30 Doradus
We report on extremely high velocity molecular gas, up to -80 km/s relative
to the ambient medium, in the giant star-formation complex 30 Doradus in the
Large Magellanic Cloud (LMC), as observed in new 22 GHz H2O maser emission
spectra obtained with the Mopra radio telescope. The masers may trace the
velocities of protostars, and the observed morphology and kinematics indicate
that current star formation occurs near the interfaces of colliding
stellar-wind blown bubbles. The large space velocities of the protostars and
associated gas could result in efficient mixing of the LMC. A similar mechanism
in the Milky Way could seed the galactic halo with relatively young stars and
gas.Comment: 11 pages plus 1 PS and 1 EPS figure, uses AASTeX preprint style;
accepted for publication in Astrophysical Journal Letter
High Resolution Mid-Infrared Imaging of Radio Ultra-Compact HII Regions
We present data from mid-infrared Keck Telescope imaging of 18 radio-selected
ultra-compact HII region candidates at diffraction-limited resolution. The goal
of these observations is to determine the sizes, luminosities, and morphologies
of the mid-infrared emitting dust surrounding the stellar sources. All 18
sources were imaged at 11.7um and at 17.65um, and 10 of them were imaged also
at 24.5um. All the sources were resolved. We have generated dust temperature
and optical depth maps and combine them with radial velocity measurements and
radio data (1.4 and 5 GHz) to constrain the properties of these star-forming
regions. Half of our objects are excited by B-stars, and all our objects have
derived types that are later than an O6 star. We find a significant correlation
between infrared and radio flux densities, and a weaker one between infrared
diameters and the central source ionizing photon rates. This latter correlation
suggests that the more compact sources result from later spectral types rather
than young age. Our new data may suggest a revision to infrared color selection
criteria of ultra-compact HII regions at resolutions <1". These 18 sources are
part of a sample of 687 sources dominated by ultra-compact HII regions selected
by matching radio and infrared maps of the first Galactic quadrant by Giveon
and coworkers. The new mid-infrared images constitute a significant improvement
in resolving sub-structure at these wavelengths. If applied to all of this
sample our analysis will improve our understanding of embedded star-formation
in the Galaxy.Comment: 66 pages, 34 figures. Accepted for publication in A
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