255 research outputs found
A Case Study on the Adoption of Measurable Agile Software Development Process
Agile methodologies for software development meet the challenges
of the current highly dynamic and competitive business environment.
The aim of this case study is to improve existing software development
process in a project for the public administration, following the basic principles of agile methodologies. Appropriate metrics for continuous
evaluation of the process are introduces to help evaluating and improving the methodology. The main objectives of the new methodology
are to improve communication with customers, to improve communication
among different distributed teams and inside the teams, and to continuously evaluate the way software is developed through selection and usage of software metrics. The paper presents the results of methodology
adoption in two subsequent iterations of a real project
Particle motion in weak relativistic gravitational fields
We derive the geodesic equation of motion in the presence of weak
gravitational fields produced by relativistic sources such as cosmic strings,
decomposed into scalar, vector and tensor parts. We find that the vector
(gravito-magnetic) force is an important contributor, and for non-relativistic
particles we recover the well-known result for the impulse from a moving
straight string. Our results can be straightforwardly incorporated into N-body
simulations to allow for the presence of cosmic defects or other sources of
weak gravitational fields.Comment: 9 pages, 5 figure
Stereotactic neuronavigation-assisted evacuation of intracranial abscess localized in the thalamus. A case report
Introduction: A brain abscess is a localized focal area of intracerebral infection that develops into a collection of pus surrounded by a well vascularized capsule. It has a rare incidence of 2% of all space occupying lesions and the deep-seated thalamus as a location is reported in 1.3 to 6% of all brain abscesses. The use of stereotactic neuronavigation-guided surgical evacuation is a minimally invasive option for achieving good treatment results.Materials and Methods: A 67-year-old female with constant headache, vertigo, staggering and muscle weakness for the right leg developed memory problems and confusion few days prior to admission in the Department of Neurosurgery. Upon examination, raised intracranial pressure, right-sided spastic hemiparesis, and memory and cognitive disturbance were present. The laboratory results showed leukocytosis, elevated glucose, cholesterol and C-reactive protein levels. A computed tomography (CT) scan showed a circular ring-like lesion localized in the region of the left thalamus that enhanced its peripheral hyperdensity after contrast application. Neuronavigation-assisted surgical evacuation was executed. A biopsy needle was inserted in the left thalamic region and the evacuated sample was sent for pathological and microbiological examinations.Results: The lesion was verified as an abscess and antibiotic therapy was prescribed for 20 days based upon the isolated bacterium and its sensitivity.Conclusion: An abscess localized in the deep-seated region of the brain is a diagnostic and therapeutic challenge. Frameless neuronavigation-guided surgical procedure is an elegant option for minimally invasive approach that allows evacuation and additional examination for correct diagnosis and effective treatment
Zone center phonons of the orthorhombic RMnO3 (R = Pr, Eu, Tb, Dy, Ho) perovskites
A short range force constant model (SRFCM) has been applied for the first
time to investigate the phonons in RMnO3 (R = Pr, Eu, Tb, Dy, Ho) perovskites
in their orthorhombic phase. The calculations with 17 stretching and bending
force constants provide good agreement for the observed Raman frequencies. The
infrared frequencies have been assigned for the first time.
PACS Codes: 36.20.Ng, 33.20.Fb, 34.20.CfComment: 8 pages, 1 figur
General solutions of Einstein's spherically symmetric gravitational equations with junction conditions
Einstein's spherically symmetric interior gravitational equations are
investigated. Following Synge's procedure, the most general solution of the
equations is furnished in case and are prescribed. The
existence of a total mass function, , is rigorously proved. Under
suitable restrictions on the total mass function, the Schwarzschild mass
, implicitly defines the boundary of the spherical body as .
Both Synge's junction conditions as well as the continuity of the second
fundamental form are examined and solved in a general manner. The weak energy
conditions for an \emph{arbitrary boost} are also considered. The most general
solution of the spherically symmetric anisotropic fluid model satisfying both
junction conditions is furnished. In the final section, various exotic
solutions are explored using the developed scheme including gravitational
instantons, interior -domains and -dimensional generalizations.Comment: 23 pages, 1 figure, uses AMS packages. Updated version has corrected
typos as well as added comments and extension regarding ISLD junction
conditions. Accepted for publication in Journal of Mathematical Physic
Moduli spaces of reflexive sheaves of rank 2
Let \sF be a coherent rank 2 sheaf on a scheme Y \subset \proj{n} of
dimension at least two. In this paper we study the relationship between the
functor which deforms a pair (\sF,\sigma), \sigma \in H^0(\sF), and the functor
which deforms the corresponding pair (X,\xi) given as in the Serre
correspondence. We prove that the scheme structure of e.g. the moduli scheme
M_Y(P) of stable sheaves on a threefold Y at (\sF), and the scheme structure at
(X) of the Hilbert scheme of curves on Y are closely related. Using this
relationship we get criteria for the dimension and smoothness of M_Y(P) at
(\sF), without assuming Ext^2(\sF,\sF) = 0. For reflexive sheaves on Y =
\proj{3} whose deficiency module M = H_{*}^1(\sF) satisfies Ext^2(M,M) = 0 in
degree zero (e.g. of diameter at most 2), we get necessary and sufficient
conditions of unobstructedness which coincide in the diameter one case. The
conditions are further equivalent to the vanishing of certain graded Betti
numbers of the free graded minimal resolution of H_{*}^0(\sF). It follows that
every irreducible component of M_{\proj{3}}(P) containing a reflexive sheaf of
diameter one is reduced (generically smooth). We also determine a good lower
bound for the dimension of any component of M_{\proj{3}}(P) which contains a
reflexive stable sheaf with "small" deficiency module M.Comment: 19 page
Tracing the Reionization-Epoch Intergalactic Medium with Metal Absorption Lines
IGM metal absorption lines observed in z>6 spectra offer the opportunity to
probe early feedback processes, the nature of enriching sources, and the
topology of reionization. We run high-resolution cosmological simulations
including galactic outflows to study the observability and physical properties
of 5 ions (C II, C IV, O I, Si II, Si IV) in absorption between z=8->5. We
apply three cases for ionization conditions: Fully neutral, fully reionized,
and a patchy model based on the flux from the nearest galaxy. We find that our
simulations broadly fit available z~5-6 IGM metal-line data, although all
observations cannot be accommodated with a single ionization condition.
Variations in O I absorbers among sight lines seen by Becker et al. (2006)
suggest significant neutral IGM patches down to z~6. Strong C IV absorbers at
z~6 may be the result of ionization by their parent galaxy. Our outflows have
typical speeds of ~200 km/s and mass loading factors of ~6. Such high mass
loading is critical for enriching the IGM to the observed levels while
curtailing star formation to match the observed z~6 rest-frame UV luminosity
function. The volume filling factor of metals increases during this epoch, but
only reaches ~1% for Z>10^(-3) Zsolar by z=5. C IV is an ideal tracer of IGM
metals at z~5-6, with dropping global ionization fractions to either higher or
lower redshifts. This results in a strongly increasing global Omega(C IV) from
z=8->5, in contrast to its relative constancy from z=5->2. Our simulations do
not support widespread early IGM enrichment from e.g. Pop III stars. High-z
absorbers arise from metals on their first outward journey from galaxies, at
distances less than 50 kpc. The galaxies responsible for early IGM enrichment
have typical M*=10^(7.0-8.5) Msolar.Comment: Accepted to MNRAS, 34 pages, 24 figures, 1 table (Sections 5.5,
6.3.1, & 6.3.2 added as well as 5 figures and 1 table
AGN Jet-induced Feedback in Galaxies. II. Galaxy colours from a multicloud simulation
We study the feedback from an AGN on stellar formation within its host
galaxy, mainly using one high resolution numerical simulation of the jet
propagation within the interstellar medium of an early-type galaxy. In
particular, we show that in a realistic simulation where the jet propagates
into a two-phase ISM, star formation can initially be slightly enhanced and
then, on timescales of few million years, rapidly quenched, as a consequence
both of the high temperatures attained and of the reduction of cloud mass
(mainly due to Kelvin-Helmholtz instabilities). We then introduce a model of
(prevalently) {\em negative} AGN feedback, where an exponentially declining
star formation is quenched, on a very short time scale, at a time t_AGN, due to
AGN feedback. Using the Bruzual & Charlot (2003) population synthesis model and
our star formation history, we predict galaxy colours from this model and match
them to a sample of nearby early-type galaxies showing signs of recent episodes
of star formation (Kaviraj et al. 2007). We find that the quantity t_gal -
t_AGN, where t_gal is the galaxy age, is an excellent indicator of the presence
of feedback processes, and peaks significantly around t_gal - t_AGN \approx
0.85 Gyr for our sample, consistent with feedback from recent energy injection
by AGNs in relatively bright (M_{B} \lsim -19) and massive nearby early-type
galaxies. Galaxies that have experienced this recent feedback show an
enhancement of 3 magnitudes in NUV(GALEX)-g, with respect to the unperturbed,
no-feedback evolution. Hence they can be easily identified in large combined
near UV-optical surveys.Comment: 18 pages, 16 figures, accepted for publication on MNRAS. This version
includes revisions after the referee's repor
Inside-out or Outside-in: The topology of reionization in the photon-starved regime suggested by Lyman-alpha forest data
We use a set of semi-numerical simulations based on Zel'dovich approximation,
friends-of-friends algorithm and excursion set formalism to generate
reionization maps of high dynamic range with a range of assumptions regarding
the distribution and luminosity of ionizing sources and the spatial
distribution of sinks for the ionizing radiation. We find that ignoring the
inhomogeneous spatial distribution of regions of high gas density where
recombinations are important -- as is often done in studies of this kind -- can
lead to misleading conclusions regarding the topology of reionization,
especially if reionization occurs in the photon-starved regime suggested by Lya
forest data. The inhomogeneous spatial distribution of recombinations
significantly reduces the mean free path of ionizing photons and the typical
size of coherently ionized regions. Reionization proceeds then much more as an
outside-in process. Low-density regions far from ionizing sources become
ionized before regions of high gas density not hosting sources of ionizing
radiation. The spatial distribution of sinks of ionization radiation also
significantly affects shape and amplitude the power spectrum of fluctuations of
21cm emission. The slope of the 21cm power spectrum as measured by upcoming
21cm experiments should be able to distinguish to what extent the topology of
reionization proceeds outside-in or inside-out while the evolution of the
amplitude of the power spectrum with increasing ionized mass fraction should be
sensitive to the spatial distribution and the luminosity of ionizing sources.Comment: Accepted in MNRAS. Revised for clarification, matches the accepted
versio
Self-trapped Exciton and Franck-Condon Spectra Predicted in LaMnO
Because the ground state has cooperative Jahn-Teller order, electronic
excitations in LaMnO are predicted to self-trap by local rearrangement of
the lattice. The optical spectrum should show a Franck-Condon series, that is,
a Gaussian envelope of vibrational sidebands. Existing data are reinterpreted
in this way. The Raman spectrum is predicted to have strong multiphonon
features.Comment: 5 pages with two embedded postscript figure
- …