12,394 research outputs found
Editorial: Advances in Invasive and Non-invasive Brain Stimulation for Dystonia and Other Hyperkinetic Movement Disorders
No abstract availabl
The Waldschmidt constant for squarefree monomial ideals
Given a squarefree monomial ideal , we show
that , the Waldschmidt constant of , can be expressed as
the optimal solution to a linear program constructed from the primary
decomposition of . By applying results from fractional graph theory, we can
then express in terms of the fractional chromatic number of
a hypergraph also constructed from the primary decomposition of . Moreover,
expressing as the solution to a linear program enables us
to prove a Chudnovsky-like lower bound on , thus verifying a
conjecture of Cooper-Embree-H\`a-Hoefel for monomial ideals in the squarefree
case. As an application, we compute the Waldschmidt constant and the resurgence
for some families of squarefree monomial ideals. For example, we determine both
constants for unions of general linear subspaces of with few
components compared to , and we find the Waldschmidt constant for the
Stanley-Reisner ideal of a uniform matroid.Comment: 26 pages. This project was started at the Mathematisches
Forschungsinstitut Oberwolfach (MFO) as part of the mini-workshop "Ideals of
Linear Subspaces, Their Symbolic Powers and Waring Problems" held in February
2015. Comments are welcome. Revised version corrects some typos, updates the
references, and clarifies some hypotheses. To appear in the Journal of
Algebraic Combinatoric
First Ex-Vivo Validation of a Radioguided Surgery Technique with beta- Radiation
Purpose: A radio-guided surgery technique with beta- -emitting radio-tracers
was suggested to overcome the effect of the large penetration of gamma
radiation. The feasibility studies in the case of brain tumors and abdominal
neuro-endocrine tumors were based on simulations starting from PET images with
several underlying assumptions. This paper reports, as proof-of-principle of
this technique, an ex-vivo test on a meningioma patient. This test allowed to
validate the whole chain, from the evaluation of the SUV of the tumor, to the
assumptions on the bio-distribution and the signal detection.
Methods: A patient affected by meningioma was administered 300 MBq of
90Y-DOTATOC. Several samples extracted from the meningioma and the nearby Dura
Mater were analyzed with a beta- probe designed specifically for this
radio-guided surgery technique. The observed signals were compared both with
the evaluation from the histology and with the Monte Carlo simulation.
Results: we obtained a large signal on the bulk tumor (105 cps) and a
significant signal on residuals of 0.2 ml (28 cps). We also show that
simulations predict correctly the observed yields and this allows us to
estimate that the healthy tissues would return negligible signals (~1 cps).
This test also demonstrated that the exposure of the medical staff is
negligible and that among the biological wastes only urine has a significant
activity.
Conclusions: This proof-of-principle test on a patient assessed that the
technique is feasible with negligible background to medical personnel and
confirmed that the expectations obtained with Monte Carlo simulations starting
from diagnostic PET images are correct.Comment: 17 pages, 4 Figs, Accepted by Physica Medic
Use of bremsstrahlung radiation to identify hidden weak beta- sources: feasibility and possible use in radio-guided surgery
The recent interest in beta- radionuclides for radio-guided surgery derives
from the feature of the beta radiation to release energy in few millimeters of
tissue. Such feature can be used to locate residual tumors with a probe located
in its immediate vicinity, determining the resection margins with an accuracy
of millimeters. The drawback of this technique is that it does not allow to
identify tumors hidden in more than few mm of tissue. Conversely, the
bremsstrahlung X-rays emitted by the interaction of the beta- radiation with
the nuclei of the tissue are relatively penetrating. To complement the beta-
probes, we have therefore developed a detector based on cadmium telluride, an
X-ray detector with a high quantum efficiency working at room temperature. We
measured the secondary emission of bremsstrahlung photons in a target of
Polymethylmethacrylate (PMMA) with a density similar to living tissue. The
results show that this device allows to detect a 1 ml residual or lymph-node
with an activity of 1 kBq hidden under a layer of 10 mm of PMMA with a 3:1
signal to noise, i.e. with a five sigma discrimination in less than 5 s
Performance of the LHCb muon system with cosmic rays
The LHCb Muon system performance is presented using cosmic ray events
collected in 2009. These events allowed to test and optimize the detector
configuration before the LHC start. The space and time alignment and the
measurement of chamber efficiency, time resolution and cluster size are
described in detail. The results are in agreement with the expected detector
performance.Comment: Submitted to JINST and accepte
The organic seed regulations framework in Europe – current status and recommendations for future development
Organic agriculture regulations, in particular European regulation EC 889/2008, prescribe the use of organically produced seed. For many cultivated plants, however, organic seed is often not available. This is mainly because investment in organic plant breeding and seed production has been low in the past. To bridge the gap between organic seed supply and demand, national and European regulations define certain circumstances under which organic producers are permitted to use non-organically produced seed. While the organic sector currently depends on these concessions, they also threaten to impede a further increase in the demand for organic seed, thereby potentially restraining present and future investment in organic seed production and plant breeding. We review the current status of the organic seed regulations framework by analysing key issues such as the role of the national derogation regimes, the role of expert groups, databases and seed prices. Key points are that (a) the situation of the organic seed sector has improved over the last few years; however, (b) reporting on organic seed to the EU by different countries needs to be harmonised; (c) the success of the organic seed sector depends critically on the implementation and improvement of national expert groups; and (d) to protect genetic diversity, the use of local varieties and landraces should not be impeded by organic seed regulations
FIRST experiment: Fragmentation of Ions Relevant for Space and Therapy
Nuclear fragmentation processes are relevant in different fields of basic research and applied physics and are of particular interest for tumor therapy and for space radiation protection applications. The FIRST (Fragmentation of Ions Relevant for Space and Therapy) experiment at SIS accelerator of GSI laboratory in Darmstadt, has been designed for the measurement of different ions fragmentation cross sections at different energies between 100 and 1000 MeV/nucleon. The experiment is performed by an international collaboration made of institutions from Germany, France, Italy and Spain. The experimental apparatus is partly based on an already existing setup made of the ALADIN magnet, the MUSIC IV TPC, the LAND2 neutron detector and the TOFWALL scintillator TOF system, integrated with newly designed detectors in the interaction Region (IR) around the carbon removable target: a scintillator Start Counter, a Beam Monitor drift chamber, a silicon Vertex Detector and a Proton Tagger for detection of light fragments emitted at large angles (KENTROS). The scientific program of the FIRST experiment started on summer 2011 with the study of the 400 MeV/nucleon 12C beam fragmentation on thin (8mm) carbon targe
A pharmacokinetic and pharmacodynamic study on metronomic irinotecan in metastatic colorectal cancer patients
The pharmacokinetics (PK) and pharmacodynamics (PD) of metronomic irinotecan have not been studied in cancer patients. The aim of the study is to investigate the PK/PD profile of irinotecan/SN-38 administered by metronomic schedule. Twenty chemotherapy-refractory or chemotherapy-resistant patients with metastatic colorectal carcinoma were enrolled. Irinotecan was infused continuously as follows: irinotecan 1.4 mg m−2 day−1 (n=7), 2.8 mg m−2 day−1 (n=5) and 4.2 mg m−2 day−1 (n=8). Drug levels were examined by HPLC, whereas ELISAs and real-time RT-PCR were used, respectively, for the measurement of plasma levels and gene expression in peripheral blood mononuclear cells of vascular endothelial growth factor/thrombospondin-1. Pharmacokinetic analysis demonstrated that the steady-state levels (Css) of SN-38 were between 1 and 3.3 ng ml−1. From a PD point of view, higher thrombospondin-1 (TSP-1) plasma levels (153.4±30.1 and 130.4±9.2% at day 49 vs pretreatment values at 1.4 and 2.8 mg m−2 day−1 dose levels, respectively) and increased gene expression in PBMC were found during the metronomic irinotecan infusion, especially at the lower doses. Four patients (20%) obtained a stable disease (median 3.9 months) despite progressing during previous standard irinotecan schedule. Toxicities >grade 1 were not observed. Metronomic irinotecan administration is very well tolerated and induces an increase of gene expression and plasma concentration of TSP-1 at low plasma SN-38 concentrations
First evidence for a major cover crop effect on arbuscular mycorrhizal fungi and organic maize growth
Arbuscular mycorrhizal fungi are increasingly used in organic cropping systems to increase yields. Although cover crops are largely used in organic farming, there is little knowledge on the impact of cover crops on native mycorrhizal fungi. Here, we studied the effect of cover crop diversity on mycorrhizal colonization in subsequent organic maize cultivars differing in the level of genetic diversity. Experiments were conducted from 2010 to 2012 in a Mediterranean environment. First Indian mustard (Brassica juncea L. Czern.), hairy vetch (Vicia villosa Roth), a mix of seven cover crop species (Mix), and natural vegetation (Control) were cultivated as winter cover crops. Then, an organically and a conventionally bred maize hybrid and three organically bred composite cross populations were cultivated. Mycorrhizal propagule dynamics were measured. Results at juvenile stage show a higher mycorrhizal colonization in maize plants grown after hairy vetch, of 35.0 %, and Mix cover crops, of 29.4 %, compared to Indian mustard, of 20.9 %, and Control, of 21.3 %. The potential of soil mycorrhization decreased of 56.5 % following Indian mustard, higher than that of other cover crops, of 34.1–47.3 %. This finding could be explained by the release of isothiocyanates in soils. Moreover, maize shoot biomass, nitrogen, and phosphorus content across all maize genotypes at juvenile stage increased with mycorrhizal colonization. These findings provide the first evidence of the greater role played by cover crop identity in the enhancement of early mycorrhizal colonization of the subsequent crop and of soil mycorrhizal activity
Performance of upstream interaction region detectors for the FIRST experiment at GSI
The FIRST (Fragmentation of Ions Relevant for Space and Therapy) experiment at GSI has been designed to study carbon fragmentation, measuring 12C double differential cross sections (∂2σ/ ∂θ∂E) for different beam energies between 100 and 1000 MeV/u. The experimental setup integrates newly designed detectors in the, so called, Interaction Region around the graphite target. The Interaction Region upstream detectors are a 250 μm thick scintillator and a drift chamber optimized for a precise measurement of the ions interaction time and position on the target. In this article we review the design of the upstream detectors along with the preliminary results of the data taking performed on August 2011 with 400 MeV/u fully stripped carbon ion beam at GSI. Detectors performances will be reviewed and compared to those obtained during preliminary tests, performed with 500 MeV electrons (at the BTF facility in the INFN Frascati Laboratories) and 80 MeV/u protons and carbon ions (at the INFN LNS Laboratories in Catania)
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