775 research outputs found
Minimal Castelnuovo-Mumford regularity for a given Hilbert polynomial
Let be an algebraically closed field of null characteristic and a
Hilbert polynomial. We look for the minimal Castelnuovo-Mumford regularity
of closed subschemes of projective spaces over with Hilbert
polynomial . Experimental evidences led us to consider the idea that
could be achieved by schemes having a suitable minimal Hilbert
function. We give a constructive proof of this fact. Moreover, we are able to
compute the minimal Castelnuovo-Mumford regularity of
schemes with Hilbert polynomial and given regularity of the
Hilbert function, and also the minimal Castelnuovo-Mumford regularity of
schemes with Hilbert function . These results find applications in the study
of Hilbert schemes. They are obtained by means of minimal Hilbert functions and
of two new constructive methods which are based on the notion of
growth-height-lexicographic Borel set and called ideal graft and extended
lifting.Comment: 21 pages. Comments are welcome. More concise version with a slight
change in the title. A further revised version has been accepted for
publication in Experimental Mathematic
Borel Degenerations of Arithmetically Cohen-Macaulay curves in P^3
We investigate Borel ideals on the Hilbert scheme components of
arithmetically Cohen-Macaulay (ACM) codimension two schemes in P^n. We give a
basic necessary criterion for a Borel ideal to be on such a component. Then
considering ACM curves in P^3 on a quadric we compute in several examples all
the Borel ideals on their Hilbert scheme component. Based on this we conjecture
which Borel ideals are on such a component, and for a range of Borel ideals we
prove that they are on the component.Comment: 20 pages, shorter and more effective versio
Rotation of Low-mass Stars in Taurus with K2
We present an analysis of K2 light curves (LCs) from Campaigns 4 and 13 for members of the young (~3 Myr) Taurus association, in addition to an older (~30 Myr) population of stars that is largely in the foreground of the Taurus molecular clouds. Out of 156 of the highest-confidence Taurus members, we find that 81% are periodic. Our sample of young foreground stars is biased and incomplete, but nearly all stars (37/38) are periodic. The overall distribution of rotation rates as a function of color (a proxy for mass) is similar to that found in other clusters: the slowest rotators are among the early M spectral types, with faster rotation toward both earlier FGK and later M types. The relationship between period and color/mass exhibited by older clusters such as the Pleiades is already in place by Taurus age. The foreground population has very few stars but is consistent with the USco and Pleiades period distributions. As found in other young clusters, stars with disks rotate on average slower, and few with disks are found rotating faster than ~2 days. The overall amplitude of the LCs decreases with age, and higher-mass stars have generally lower amplitudes than lower-mass stars. Stars with disks have on average larger amplitudes than stars without disks, though the physical mechanisms driving the variability and the resulting LC morphologies are also different between these two classes
Analysis of GPS, VLBI and DORIS input time series for ITRF2014
In this work we have compared the Up component
time series reprocessed in view of the new ITRF2014. The solutions
that we have considered are the combinations of individual
submissions of the Operational Analysis Centers (ACs) as o-
cial IVS, IGS and IDS products.We have modelled time series as
discrete-time Marcov processes, we have detected and removed
discontinuities from data time series and estimated trends (long
term signals). A frequency analysis making research of residual
periodic signals and identification of the common ones to all the
three space geodetic techniques has been performed. Preliminary
results on co-located sites are shown
Forested Infiltration Area (FIA) Design in the Arborea Nitrate Vulnerable Zone (Sardinia, Italy)
This research aims to test a Managed Aquifer Recharge (MAR) technique based on Forested Infiltration Areas (FIAs) to reduce the groundwater nitrate contamination of a sandy phreatic aquifer in the Arborea NVZ (Sardinia, Italy). The FIA system in Arborea will be supplied with drainage water having an average NO3 concentration of 70 mg L−1, pumped from a dewatering pumping station. The water will be treated before infiltration through an innovative passive treatment system, consisting of a mixture of inert and organic materials, to attenuate organic and inorganic contamination and to prevent clogging processes at the infiltrating surface. The experiment will be conducted for a duration of two years. Monthly monitoring will define, ante operam, the quality baseline of drainage water and groundwater and will assess, post operam, the efficiency of the FIA system. An estimation of the infiltration rate in the sandy soils based on preliminary surveys showed a potential recharge rate of around 0.7 hm3 year−1 per 0.4 ha of the FIA system
Shintaido in the elderly: the new way for physical and psychological health
The research aims to investigate the effects of a Shintaido practice in terms of physical and psychological functioning in a group of elderly. Forty seniors, of both gender, with a mean age of (69 ± 6) years, self-sufficient and without highly invalidating diseases participated in the study. The experimental group (EG) attended the Shintaido physical training of 20 weeks (1 hour per session, twice a week), while the control group (CG) maintained his usual routine. The exercise protocol included specific activities of joint mobility, balance and breathing. At the begin and at the end of intervention were administered to both groups the following validated instruments: 1) One-leg Stance test for the measure of monopodalic static balance; 2) 6-Minutes Walking test for the endurance assessment; 3) Self-Efficacy Perception in Physical Activity (APEF) questionnaire for the selfefficacy evaluation. Data were treated with the not-parametric test for paired and unpaired samples, the Spearman correlation and the linear regression. The results show that: 1) the EG improves the endurance in walking and the monopodalic balance as well as his self-efficacy after the Shintaido program; 2) there are strong associations among Shintaido physical activity and physical/psychological variables; 3) there is a mediating effect of walking endurance between the participation to Shintaido training and the self-efficacy. The results suggest that a well structured Shintaido training can help to maintain a good level of physical and psychological functioning in old people
Term-ordering free involutive bases
In this paper, we consider a monomial ideal J in P := A[x1,...,xn], over a commutative ring A, and we face the problem of the characterization for the family Mf(J) of all homogeneous ideals I in P such that the A-module P/I is free with basis given by the set of terms in the Groebner escalier N(J) of J. This family is in general wider than that of the ideals having J as initial ideal w.r.t. any term-ordering, hence more suited to a computational approach to the study of Hilbert schemes. For this purpose, we exploit and enhance the concepts of multiplicative variables, complete sets and involutive bases introduced by Janet and we generalize the construction of J-marked bases and term-ordering free reduction process introduced and deeply studied for the special case of a strongly stable monomial ideal J. Here, we introduce and characterize for every monomial ideal J a particular complete set of generators F(J), called stably complete, that allows an explicit description of the family Mf(J). We obtain stronger results if J is quasi stable, proving that F(J) is a Pommaret basis and Mf(J) has a natural structure of affine scheme. The final section presents a detailed analysis of the origin and the historical evolution of the main notions we refer to
Dynamics of SNARE Assembly and Disassembly during Sperm Acrosomal Exocytosis
The dynamics of SNARE assembly and disassembly during membrane recognition and fusion is a central issue in intracellular trafficking and regulated secretion. Exocytosis of sperm's single vesicle—the acrosome—is a synchronized, all-or-nothing process that happens only once in the life of the cell and depends on activation of both the GTP-binding protein Rab3 and of neurotoxin-sensitive SNAREs. These characteristics make acrosomal exocytosis a unique mammalian model for the study of the different phases of the membrane fusion cascade. By using a functional assay and immunofluorescence techniques in combination with neurotoxins and a photosensitive Ca(2+) chelator we show that, in unactivated sperm, SNAREs are locked in heterotrimeric cis complexes. Upon Ca(2+) entry into the cytoplasm, Rab3 is activated and triggers NSF/α-SNAP-dependent disassembly of cis SNARE complexes. Monomeric SNAREs in the plasma membrane and the outer acrosomal membrane are then free to reassemble in loose trans complexes that are resistant to NSF/α-SNAP and differentially sensitive to cleavage by two vesicle-associated membrane protein (VAMP)–specific neurotoxins. Ca(2+) must be released from inside the acrosome to trigger the final steps of membrane fusion that require fully assembled trans SNARE complexes and synaptotagmin. Our results indicate that the unidirectional and sequential disassembly and assembly of SNARE complexes drive acrosomal exocytosis
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