A Sparse Johnson--Lindenstrauss Transform

Dimension reduction is a key algorithmic tool with many applications including nearest-neighbor search, compressed sensing and linear algebra in the streaming model. In this work we obtain a {\em sparse} version of the fundamental tool in dimension reduction --- the Johnson--Lindenstrauss transform. Using hashing and local densification, we construct a sparse projection matrix with just $\tilde{O}(\frac{1}{\epsilon})$ non-zero entries per column. We also show a matching lower bound on the sparsity for a large class of projection matrices. Our bounds are somewhat surprising, given the known lower bounds of $\Omega(\frac{1}{\epsilon^2})$ both on the number of rows of any projection matrix and on the sparsity of projection matrices generated by natural constructions. Using this, we achieve an $\tilde{O}(\frac{1}{\epsilon})$ update time per non-zero element for a $(1\pm\epsilon)$-approximate projection, thereby substantially outperforming the $\tilde{O}(\frac{1}{\epsilon^2})$ update time required by prior approaches. A variant of our method offers the same guarantees for sparse vectors, yet its $\tilde{O}(d)$ worst case running time matches the best approach of Ailon and Liberty.Comment: 10 pages, conference version

On sampling nodes in a network

Random walk is an important tool in many graph mining applications including estimating graph parameters, sampling portions of the graph, and extracting dense communities. In this paper we consider the problem of sampling nodes from a large graph according to a prescribed distribution by using random walk as the basic primitive. Our goal is to obtain algorithms that make a small number of queries to the graph but output a node that is sampled according to the prescribed distribution. Focusing on the uniform distribution case, we study the query complexity of three algorithms and show a near-tight bound expressed in terms of the parameters of the graph such as average degree and the mixing time. Both theoretically and empirically, we show that some algorithms are preferable in practice than the others. We also extend our study to the problem of sampling nodes according to some polynomial function of their degrees; this has implications for designing efficient algorithms for applications such as triangle counting

Link-based similarity search to fight web spam

www.ilab.sztaki.hu/websearch We investigate the usability of similarity search in fighting Web spam based on the assumption that an unknown spam page is more similar to certain known spam pages than to honest pages. In order to be successful, search engine spam never appears in isolation: we observe link farms and alliances for the sole purpose of search engine ranking manipulation. The artificial nature and strong inside connectedness however gave rise to successful algorithms to identify search engine spam. One example is trust and distrust propagation, an idea originating in recommender systems and P2P networks, that yields spam classificators by spreading information along hyperlinks from white and blacklists. While most previous results use PageRank variants for propagation, we form classifiers by investigating similarity top lists of an unknown page along various measures such as co-citation, companion, nearest neighbors in low dimensional projections and SimRank. We test our method over two data sets previously used to measure spam filtering algorithms. 1

Generalized Private Selection and Testing with High Confidence

Composition theorems are general and powerful tools that facilitate privacy accounting across multiple data accesses from per-access privacy bounds. However they often result in weaker bounds compared with end-to-end analysis. Two popular tools that mitigate that are the exponential mechanism (or report noisy max) and the sparse vector technique, generalized in a recent private selection framework by Liu and Talwar (STOC 2019). In this work, we propose a flexible framework of private selection and testing that generalizes the one proposed by Liu and Talwar, supporting a wide range of applications. We apply our framework to solve several fundamental tasks, including query releasing, top-$k$ selection, and stable selection, with improved confidence-accuracy tradeoffs. Additionally, for online settings, we apply our private testing to design a mechanism for adaptive query releasing, which improves the sample complexity dependence on the confidence parameter for the celebrated private multiplicative weights algorithm of Hardt and Rothblum (FOCS 2010).Comment: Appearing in ITCS 202

Ultragyors lineáris és nemlineáris optikai folyamatok makromolekulákon = Ultrafast linear and nonlinear optical processes on macromolecules

Mérőrendszerünkhöz új tükörkészletet és diszperzió szabályozó egységet fejlesztettünk ki, széles hullámhossz tartományban lehetővé téve (akár 40 fs-nál rövidebb) stabil fényimpulzusok keltését. Félvezető alapú telítődő abszorbens (SESAM) mintákon meghatároztuk a a fs-ps időtartományba eső tranziens abszorpció időállandóit. A kinetikai adatok kiértékelésére kidolgoztunk egy modellfüggetlen, nemparametrikus dekonvolúciós eljárást. Fotoszinetikus fénybegyűjtő komplexeken jellemeztük a fénykárosodást kivédő hődisszipáció ps-os kinetikáját. A fényenergia hasznosító bakteriorodopszin (bR) fehérjéből készített natív és módosított szárított mintákon megállapítottuk a gerjesztett állapot valamint az ultragyors intermedierek abszorpciókinetikai paramétereit. 10 fs időfelbontású koherens infravörös emissziós kísérletek alapján jellemeztük a bR retinál kromofórjának gerjesztése során létrejövő dipólmomentum változást, és az azt követő koherens vibrációs folyamatokat. Elsőként mutattuk ki és jellemeztük a bR mintából származó terahertzes emisszó jelenségét, megállapítva, hogy az részben a retinál molekula gerjesztett állapotú elektronmozgásából, részben pedig - a feltehetően ez által keltett - kezdeti funkcionális protonmozgásból származik. Kidolgoztunk egy kvantumelektrodinamikai leírást, melynek keretében a retinál gerjesztése során fellépő másodrendű optikai folyamatok egységesen tárgyalhatók. | A new mirror set and a dispersion control unit was developed for our measuring system, making possible to generate stable light pulses (of even shorter than 40 fs) in a wide range of wavelength. The fs-ps transient absorption time-constants of semiconductor saturable absorber mirror (SESAM) samples were determined. A model-independent nonparametric deconvolution procedure was elaborated for the analysis of the kinetic data. Photosynthetic light-harvesting complexes were characterized by their ps kinetics of heat dissipation process, protecting them from light-induced damages. The absorption kinetic parameters describing the excited state and the ultrafast intermediers in native and modified dried samples of bacteriorhodopsin (bR) protein - utilizing light energy - were determined. By coherent infrared emission experiments the dipole moment change upon the excitation of the retinal chromophore of bR, as well as the subsequent coherent vibration processes were characterized. The phenomenon of terahertz emission from a bR sample was demonstrated and characterized for the first time, showing that it originates both from the excited-state electron motion of the retinal molecule and the functional early proton movement, probably generated by the former process. A theoretical description was derived from quantum electrodynamics for a unified description of the second order optical processes occurring on the excitation of retinal

Conception and reality: outcome of SARS-CoV-2 infection and vaccination among Hungarian IBD patients on biologic treatments

Inflammatory bowel disease potentially elevates the risk of infections, independently from age, while the disease activity and medical treatment(s) can also increase the risks. Nevertheless, it is necessary to clarify these preconceptions as well during the COVID-19 pandemic.An observational, questionnaire based study was conducted in Hungary between February and August 2021. 2 questionnaires were completed. The first questionnaire surveyed the impact of the pandemic on patients with biologic treatments and assessed the severity and outcome of the infection, whereas the second one assessed vaccination rate and adverse events.472 patients participated in the study. 16.9% of them acquired the infection and 6.3% needed hospitalization. None of them required ICU care. Male sex elevated the risk of infection (p=0.008), while glove (p=0.02) and mask wearing (p=0.005) was the most effective prevention strategy. Nevertheless, abstaining from community visits or workplace did not have an impact on the infection rate. Smoking, age, and disease type did not elevate the risk. UC patients had poorer condition during the infection (p=0.003); furthermore, the disease activity could potentially worsen the course of infection (p=0.072). The different biological treatments were equally safe; no difference was observed in the infection rate, course of COVID-19. Azathioprine and corticosteroids did not elevate the infection rate. 28 patients (35.0%) suspended the ongoing biologic treatment, but it had no impact on the disease course. However, it resulted in changing the current treatment (p=0.004). 9.8% of the respondents were sceptic about being vaccinated, and 90% got vaccinated. In one case, a serious flare-up occurred.Most patients acquired the infection at workplace. Biologic therapies had no effect on the COVID-19 infection, whereas male sex, an active disease, and UC could be larger threat than treatments. Vaccination was proved to be safe, and patient education is important to achieve mass vaccination of the population

Real-life efficacy of vedolizumab on endoscopic healing in inflammatory bowel disease - A nationwide Hungarian cohort study

Background: GEMINI trials demonstrated the therapeutic efficacy of vedolizumab (VDZ) in Crohn's disease (CD) and ulcerative colitis (UC).Research design and methods: Aim of this study was to determine the real-life effectiveness of VDZ on endoscopic healing in the Hungarian nationwide cohort of inflammatory bowel disease (IBD) patients based on changes on clinical and endoscopic scores. Every adult IBD patient in the country (121 UC and 83 CD) who completed short-term VDZ therapy were enrolled, of which 72 UC and 52 CD patients could complete the long-term therapy.Results: Rates of endoscopic healing were substantially higher in UC compared with CD patients during short- and long-term therapy (52.9% vs. 21.7%, p<0.0001, and 51.4% vs. 21.2%, p=0.015, respectively). In CD, the rate of endoscopic healing was lower at week 14 compared with week 22 (14.5% vs. 37.0%, p=0.026). Prior anti-TNF-alpha therapy (88.73%) was not associated with a significant decrease in therapeutic response. Average disease duration was significantly lower in CD patients achieving endoscopic healing at week 52 (11.75 vs. 5.27 years, p=0.007).Conclusions: VDZ therapy is an effective therapeutic option in anti-TNF-alpha refractory IBD. However, endoscopic healing rate was substantially lower and showed a significant delay in CD compared with UC

Kutatási füzetek 15.

Szerkesztők: Vitári Zsolt; Bene Krisztián; Sarlós István | További szerzők: Bene Adrián; Bíró Teofil; Bótor Tímea; Csabai Zoltán; Gonda Gábor; Hosszú Csaba; Kern Tamás; Kovács Tamás; Madácsy József; Németh Nikoletta; Rab Virág; Sarlós István; Schuller Balázs; Somogyi Andrea; Szigetvári Krisztián; Vitári-Wéber Adrienn | Cím: Kutatási Füzetek 15. | Megjelenési adatok: PTE BTK Interdiszcplináris Doktori Iskola, Pécs, 2009. | ISSN: 1416-0986 | ISBN: 978-963-88505-0-8 | Megjegyzés: A Kutatási Füzetek a Pécsi Tudományegyetem Interdiszciplináris Doktori Iskolájának kiadványsorozata.(1) Bene Adrián: Jean-Paul Sartre történelemfogalma 15-30 | (2) Bíró Teofil: A hatalom legitimációjának problematikája a két világháború közötti Köztes-Európában 31-53 | (3) Bótor Tímea: A „Moszkva-Harmadik Róma” elmélet megalapozottsága a legújabb szakirodalom tükrében 55-70 | (4) Csabai Zoltán: Egy különös hitelszerződés I. Dareiosz korából 71-80 | (5) Gonda Gábor: Ki volt „hűséges a hazához”? A „nemzethűség” megállapításának problematikája Tolna vármegye Völgységi járásában 81-102 | (6) Hosszú Csaba: A köskönyök világa 103-120 | (7) Kern Tamás: Vázlat 10 pontban a rendszerváltás utáni védelem- és katonapolitikáról 121-138 | (8) Kovács Tamás: Vitéz Kisbarnaki Farkas Ferenc élete 139-155 | (9) Madácsy József: Gregory Bateson és az Anonim Alkoholisták 157-171 | (10) Németh Nikoletta: A Jobboldali Ellenzék közigazgatási programja 173-187 | (11) Rab Virág: Két elképzelés Európa kilátásairól az első világháborút követően 189-209 | (12) Sarlós István: Az alsó-Duna-völgyi Duna menti kisvárosok mezőgazdasága a két világháború között - Dunaföldvár mezőgazdasága az 1930-as években 211-232 | (13) Schuller Balázs: Munkásönigazgatás a Bakonyban - 1956 eseményei a Halimbai Bauxitbányánál 233-252 | (14) Somogyi Andrea: Az őshaza és a pogány múlt ábrázolása Prágai Cosmas krónikájában 253-261 | (15) Szigetvári Krisztián: Vázlat Primo de Rivera diktatúrájáról (1923. szeptember – 1930. január) 263-279 | (16) Vitári–Wéber Adrienn: Vázlatok egy pécsi amatőr régész pályafutásának kezdeteihez a 19. század második felében - Dr. Horváth Antal (1848–1912) régészeti jellegű tevékenységének adatolható kezdetei kiadatlan levelezések alapján (1866–1867) 281-30