Positivity of Chern Classes for Reflexive Sheaves on P^N

It is well known that the Chern classes $c_i$ of a rank $n$ vector bundle on \PP^N, generated by global sections, are non-negative if $i\leq n$ and vanish otherwise. This paper deals with the following question: does the above result hold for the wider class of reflexive sheaves? We show that the Chern numbers $c_i$ with $i\geq 4$ can be arbitrarily negative for reflexive sheaves of any rank; on the contrary for $i\leq 3$ we show positivity of the $c_i$ with weaker hypothesis. We obtain lower bounds for $c_1$, $c_2$ and $c_3$ for every reflexive sheaf \FF which is generated by H^0\FF on some non-empty open subset and completely classify sheaves for which either of them reach the minimum allowed, or some value close to it.Comment: 16 pages, no figure

Technological innovation vs technological backwardness patterns in latecomer firms: An absorptive capacity perspective

This study investigates the factors inhibiting latecomer firms’ technological innovation and eventually their catch-up process. Accordingly, it relies on resource-based theory to advance an absorptive capacity argument and develop a multiple mediation model. This model is tested using the data collected from 166 Chinese manufacturing firms. Furthermore, this study provides theoretical arguments and empirical evidence about the role of each dimension of absorptive capacity in studying the catch-up process of latecomer firms, with particular reference to knowledge transformation. It also offers insights into the limitations of predominant latecomer firms’ innovation strategies and suggests shifts in managerial practice and policymaking

Certain minimal varieties are set-theoretic complete intersections

We present a class of homogeneous ideals which are generated by monomials and binomials of degree two and are set-theoretic complete intersections. This class includes certain reducible varieties of minimal degree and, in particular, the presentation ideals of the fiber cone algebras of monomial varieties of codimension two

The effect of a safety climate training on safety performance. A longitudinal study on the use of individual protective devises

The aim of this study is to explore the effectiveness on safety performance and particularly on the use of individual protective devises at work of a training concerning safety climate. Safety climate and culture research developed successfully in the last decades, showing how safety climate is a robust predictor of safety subjective outcomes, such as safety behaviour, and of objective outcomes, such as accidents and injuries. Literature shows ambiguous findings on the effectiveness of safety training and interventions to improve safety performance of employees and highlights some methodological criticality. The idea of the present study was to test the effect of a training focused on the improvement of safety climate with a longitudinal design. Data collection involved 1495 blue-collars from 6 Italian manufacturing companies. Two different types of safety climate trainings for supervisors were performed and in some cases no training was performed. A long training was scheduled in 6 weekly meetings of 4 hours each and a short one was scheduled in only one meeting of 3 hours. In 3 companies of the sample safety climate and safety performance were measured twice, one before the training and one about 12 months after it. In all the companies monitoring activities on the use of individual protective devises were conducted. The research evidenced that safety climate training does not always help to reduce the number of unsafe behaviours, but a moderation effect of safety climate seems to inflect the relation between training and performance. Particularly, in work-groups with a high safety climate a positive effect of the training always was found

Longitudinal Assessment of Critical Thinking Skills Across a Dental Curriculum

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/153614/1/jddjde018088.pd

Variable X-ray absorption in the mini-BAL QSO PG 1126-041

X-ray studies of active galactic nuclei (AGN) with powerful nuclear winds are important for constraining the physics of the inner accretion/ejection flow around supermassive black holes (SMBHs) and for understanding the impact of such winds on the AGN environment. Our main scientific goal is to constrain the properties of the circum-nuclear matter close to the SMBH in the mini-broad absorption line quasar (mini-BAL QSO) PG 1126-041 using a multi-epoch observational campaign with XMM-Newton. We performed temporally resolved X-ray spectroscopy and simultaneous UV and X-ray photometry on the most complete set of observations and on the deepest X-ray exposure of a mini-BAL QSO ever. We found complex X-ray spectral variability on time scales of both months and hours, which is best reproduced by means of variable massive ionized absorbers along the line of sight. As a consequence, the observed optical-to-X-ray spectral index is found to be variable with time. In the highest signal-to-noise observation we detected highly ionized X-ray absorbing material outflowing much faster (v ~ 16500 km/s) than the UV absorbing one (v ~ 5000 km/s). This highly ionized absorber is found to be variable on very short (a few kiloseconds) time scales. Our findings are qualitatively consistent with line-driven accretion disk winds scenarios. Our observations have opened the time-resolved X-ray spectral analysis field for mini-BAL QSOs. Only with future deep studies will we be able to map the dynamics of the inner flow and understand the physics of AGN winds and their impact on the environment.Comment: Replaced to match the published versio

HOW TO OVERCOME ANALPHABETISM IN READING CHINESE CHARACTER

Most languages in the world use some system of alphabetical characters: Latin, Greek, Cyrillic, Hebrew, Arabic, Hindi and so on. A foreigner that does not know the language can get some information from a written text provided he knows the alphabet and disposes of a dictionary. When there is no longer an alphabet, but only pictorial characters, the problem becomes at first unsolvable. Chinese is the main language where an ignorant foreigner is completely analphabet. Fortunately there are methods that after some training allow the recognition of pictorial characters. In our university some twenty pupils of the Excellence School participated to an experiment of Chinese alphabetization gluing a traditional practical Chinese first course with information theory methods for dealing with image data bases. In this article first we discuss both the theoretical foundations. Then we give a report of the merging of the two conceptual schemes as it was performed at the excellence school. Finally we draw some conclusions about improvements of the method