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Search Results: 1 - 10 of 401137 matches for " M. Jurczak "
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Intellectual Capital Measurement Methods
Jolanta Jurczak
Economics and Organization of Future Enterprise , 2008, DOI: 10.2478/v10061-008-0005-y
Abstract: Enterprise efficiency and competitiveness depend on intellectual resources, as well as the ability to apply them in the market competition. Intellectual capital of a company may be used more effectively when identification and measurement of its components are possible. The article presents a classified and grouped review of different Intellectual Capital Measurement Methods describing them and providing companies with information about a variety of ways and advice how to choose a proper measurement method.
A universal expectation bound on empirical projections of deformed random matrices
Kamil Jurczak
Mathematics , 2012, DOI: 10.1007/s10959-013-0517-9
Abstract: Let $C$ be a real-valued $M\times M$ matrix with singular values $\lambda_1\ge...\ge\lambda_M$ and $E$ a random matrix of centered i.i.d. entries with finite fourth moment. In this paper we give a universal upper bound on the expectation of $||\hat\pi_rX||_{S_2}^2-||\pi_rX||^2_{S_2}$, where $X:=C+E$ and $\hat\pi_r$ (resp. $\pi_r$) is a rank-$r$ projection maximizing the Hilbert-Schmidt norm $||\tilde\pi_rX||_{S_2}$ (resp. $||\tilde\pi_rC||_{S_2}$) over the set $\S_{M,r}$ of all orthogonal rank-$r$ projections. This result is a generalization of a theorem for Gaussian matrices due to Rohde (2012). Our approach differs substantially from the techniques of the mentioned article. We analyze $||\hat\pi_rX||_{S_2}^2-||\pi_rX||^2_{S_2}$ from a rather deterministic point of view by an upper bound on $||\hat\pi_rX||_{S_2}^2-||\pi_rX||^2_{S_2}$, whose randomness is totally determined by the largest singular value of $E$.
The critical threshold level on Kendall's tau statistic concerning minimax estimation of sparse correlation matrices
Kamil Jurczak
Statistics , 2014,
Abstract: In a sparse high-dimensional elliptical model we consider a hard threshold estimator for the correlation matrix based on Kendall's tau with threshold level $\alpha(\frac{\log p}{n})^{1/2}$. Parameters $\alpha$ are identified such that the threshold estimator achieves the minimax rate under the squared Frobenius norm and the squared spectral norm. This allows a reasonable calibration of the estimator without any quantitative information about the tails of the underlying distribution. For Gaussian observations we even establish a critical threshold constant $\alpha^\ast$ under the squared Frobenius norm, i.e. the proposed estimator attains the minimax rate for $\alpha>\alpha^\ast$ but in general not for $\alpha<\alpha^\ast$. To the best of the author's knowledge this is the first work concerning critical threshold constants. The main ingredient to provide the critical threshold level is a sharp large deviation expansion for Kendall's tau sample correlation evolved from an asymptotic expansion of the number of permutations with a certain number of inversions. The investigation of this paper also covers further statistical problems like the estimation of the latent correlation matrix in the transelliptical and nonparanormal family.
Weak convergence of the empirical spectral distribution of ultra-high-dimensional banded sample covariance matrices
Kamil Jurczak
Statistics , 2015,
Abstract: In this article we investigate high-dimensional banded sample covariance matrices under the regime that the sample size $n$, the dimension $p$ and the bandwidth $d$ tend simultaneously to infinity such that $$n/p\to 0 \ \ \text{and} \ \ 2d/n\to y>0.$$ It is shown that the empirical spectral distribution of those matrices almost surely converges weakly to some deterministic probability measure which is characterized by its moments. Certain restricted compositions of natural numbers play a crucial role in the evaluation of the expected moments of the empirical spectral distribution.
Polscy przedsiebiorcy w Dolinie Krzemowej
Dominika Latusek-Jurczak
Management and Business Administration. Central Europe , 2013, DOI: 10.7206/mba.ce.2084.3356.44
Abstract: Purpose: This text is a review of the results of a research project on Polish entrepreneurs and Polish enterprises in Silicon Valley, conducted by the author in Silicon Valley in The United States in the years 2007–2012.Methodology: 81 participants took part in the research (members of 13 different companies and several government and third sector organizations). Among the organizations represented in the project there were companies established in the Valley by Poles, Polish companies present in the Valley, as well as institutions that are active in promotion and support of Polish business presence in the United States, especially in Silicon Valley.Findings: The research indicates that there are three main areas for improvement in Poland, if it is to be home to companies characterized by a potential for rapid growth (as the ones that Silicon Valley is famous for). The first one concerns cultural aspects associated with low tolerance of risk and social censure of those who fail in business. The second includes financing, in particular limited access to venture capital and business angels networks. The third one refers to business education of entrepreneurs, for whom gaining practical experiences in world-class centers of entrepreneurship, such as Silicon Valley, is of utmost importance.
Spectral analysis of high-dimensional sample covariance matrices with missing observations
Kamil Jurczak,Angelika Rohde
Statistics , 2015,
Abstract: We study high-dimensional sample covariance matrices based on independent random vectors with missing coordinates. The presence of missing observations is common in modern applications such as climate studies or gene expression micro-arrays. A weak approximation on the spectral distribution in the "large dimension $d$ and large sample size $n$" asymptotics is derived for possibly different observation probabilities in the coordinates. The spectral distribution turns out to be strongly influenced by the missingness mechanism. In the null case under the missing at random scenario where each component is observed with the same probability $p$, the limiting spectral distribution is a Mar\v{c}enko-Pastur law shifted by $(1-p)/p$ to the left. As $d/n\rightarrow y< 1$, the almost sure convergence of the extremal eigenvalues to the respective boundary points of the support of the limiting spectral distribution is proved, which are explicitly given in terms of $y$ and $p$. Eventually, the sample covariance matrix is positive definite if $p$ is larger than $$ 1-\left(1-\sqrt{y}\right)^2, $$ whereas this is not true any longer if $p$ is smaller than this quantity.
Transport spectroscopy of a single dopant in a gated silicon nanowire
H. Sellier,G. P. Lansbergen,J. Caro,N. Collaert,I. Ferain,M. Jurczak,S. Biesemans,S. Rogge
Physics , 2006, DOI: 10.1103/PhysRevLett.97.206805
Abstract: We report on spectroscopy of a single dopant atom in silicon by resonant tunneling between source and drain of a gated nanowire etched from silicon on insulator. The electronic states of this dopant isolated in the channel appear as resonances in the low temperature conductance at energies below the conduction band edge. We observe the two possible charge states successively occupied by spin-up and spin-down electrons under magnetic field. The first resonance is consistent with the binding energy of the neutral $D^0$ state of an arsenic donor. The second resonance shows a reduced charging energy due to the electrostatic coupling of the charged $D^-$ state with electrodes. Excited states and Zeeman splitting under magnetic field present large energies potentially useful to build atomic scale devices.
Sub-threshold channels at the edges of nanoscale triple-gate silicon transistors
H. Sellier,G. P. Lansbergen,J. Caro,N. Collaert,I. Ferain,M. Jurczak,S. Biesemans,S. Rogge
Physics , 2006, DOI: 10.1063/1.2476343
Abstract: We investigate by low-temperature transport experiments the sub-threshold behavior of triple-gate silicon field-effect transistors. These three-dimensional nano-scale devices consist of a lithographically defined silicon nanowire surrounded by a gate with an active region as small as a few tens of nanometers, down to 50x60x35 nm^3. Conductance versus gate voltage show Coulomb-blockade oscillations with a large charging energy due to the formation of a small potential well below the gate. According to dependencies on device geometry and thermionic current analysis, we conclude that sub-threshold channels, a few nanometers wide, appear at the nanowire edges, hence providing an experimental evidence for the corner-effect.
Advanced CMOS device technologies for 45 nm node and below
A. Veloso, T. Hoffmann, A. Lauwers, H. Yu, S. Severi, E. Augendre, S. Kubicek, P. Verheyen, N. Collaert, P. Absil, M. Jurczak and S. Biesemans
Science and Technology of Advanced Materials , 2007,
Abstract: We review and discuss the latest developments and technology options for 45 nm node and below, with scaled planar bulk MOSFETs and MuGFETs as emerging devices. One of the main metal gate (MG) candidates for scaled CMOS technologies are fully silicided (FUSI) gates. In this work, by means of a selective and controlled poly etch-back integration process, dual work-function Ni-based FUSI/HfSiON CMOS circuits with record ring oscillator performance (high-VT) are reported (17 ps at VDD=1.1 V and 20 pA/μm Ioff), meeting the ITRS 45 nm node requirement for low-power (LP) CMOS. Compatibility of FUSI and other MG with known stress boosters like stressed CESL (contact-etch-stop-layer with high intrinsic stress) or embedded SiGe in the pMOS S/D regions is validated. To obtain MuGFET devices that are competitive, as compared to conventional planar bulk devices, and that meet the stringent drive and leakage current requirements for the 32 nm node and beyond, higher channel mobilities are required. Results obtained by several strain engineering methods are presented here.
Laparoscopic Cholecystectomy Combined Using Miniaturised Instruments in Transgastric Gall Bladder Removal: Performed on 63 Patients
Florent Jurczak,Jean-Paul Pousset
Minimally Invasive Surgery , 2010, DOI: 10.1155/2010/582763
Abstract: Background. The laparoscopic cholecystectomy is a perfectly codified surgical procedure. The development of recent innovative and experimental surgical techniques Natural Orifice transluminal endoscopic surger (N.O.T.E.S.) which reduces the abdominal wall trauma leads us to develop a combined procedure of a standard dissection using miniaturised instruments already existing on the market (3 and 5?mm wide) and a gall bladder removal through a short gastrotomy Natural Orifice Specimen Extraction (N.O.S.E.). Methods. Our objective was to evaluate the safety, the feasibility, and the reproducibility of our new approach. After reviewing existing products on the market and a feasibility study, we put in place a protocol in our structure for patients on whom the procedure was performed. We carried out a gall bladder removal by a short gastrotomy, located on the anterior gastric wall, which then reduced the abdominal wall trauma and allowed them to resume normal physical activity quickly without risk of trocar site hernia. Results. We performed the procedure described in this paper on 63 patients, between April 2008 and July 2009. There were 14 men and 49 women with an average age of 46.8 years (ranging from 28 to 77) and an average BMI of 27.2. 30 patients had at least one gallstone larger than 10?mm. There was no postoperative gastric or abdominal wall complication and a fast recovery for all the patients in our study. Conclusions. This procedure is feasible, reproducible, with good results and minimal abdominal wall trauma. It is also safer than N.O.T.E.S. and endoscopic clipping and recovery, allowing normal physical activity, fast and, without risk of incisional hernia. 1. Introduction The laparoscopy became the main surgical technique for cholecystectomy with a rate of laparoscopic performances of about 99% for some French teams. The development of recent innovative and experimental surgical techniques (N.O.T.E.S.) [1–4] reduces the abdominal wall trauma and complication by using ports and removal of the gall bladder or any other abdominal organs. The risk of incisional hernia increases when using a 10?mm or more port [5, 6]. The removal of an inflamed gall bladder with or without very large gallstones usually requires enlarging one of the abdominal incisions. It will be closed of course, scrupulously [7, 8], but there is always a risk of complication (infection, bruising, incisional hernia [9–11]) and that is the same problem with the single port access surgery as it is also difficult to get back to normal physical activity quickly, without risk of
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