Papers by Youssef Mohamed
arXiv (Cornell University), Jun 1, 2021
Identifying controllable aspects of the environment has proven to be an extraordinary intrinsic m... more Identifying controllable aspects of the environment has proven to be an extraordinary intrinsic motivator to reinforcement learning agents. Despite repeatedly achieving State-of-the-Art results, this approach has only been studied as a proxy to a reward-based task and has not yet been evaluated on its own. Current methods are based on action-prediction. Humans, on the other hand, assign blame to their actions to decide what they controlled. This work proposes Controlled Effect Network (CEN), an unsupervised method based on counterfactual measures of blame to identify effects on the environment controlled by the agent. CEN is evaluated in a wide range of environments showing that it can accurately identify controlled effects. Moreover, we demonstrate CEN's capabilities as intrinsic motivator by integrating it in the state-of-the-art exploration method, achieving substantially better performance than action-prediction models.
Investigative ophthalmology & visual science, 2018
The study aimed to provide a quantitative description of aqueous humor dynamics in healthy rat ey... more The study aimed to provide a quantitative description of aqueous humor dynamics in healthy rat eyes. One eye of 26 anesthetized adult Brown-Norway rats was cannulated with a needle connected to a perfusion pump and pressure transducer. Pressure-flow data were measured in live and dead eyes by varying pump rate (constant-flow technique) or by modulating pump duty cycle to hold intraocular pressure (IOP) at set levels (modified constant-pressure technique). Data were fit by the Goldmann equation to estimate conventional outflow facility (\(\def\upalpha{\unicode[Times]{x3B1}}\)\(\def\upbeta{\unicode[Times]{x3B2}}\)\(\def\upgamma{\unicode[Times]{x3B3}}\)\(\def\updelta{\unicode[Times]{x3B4}}\)\(\def\upvarepsilon{\unicode[Times]{x3B5}}\)\(\def\upzeta{\unicode[Times]{x3B6}}\)\(\def\upeta{\unicode[Times]{x3B7}}\)\(\def\uptheta{\unicode[Times]{x3B8}}\)\(\def\upiota{\unicode[Times]{x3B9}}\)\(\def\upkappa{\unicode[Times]{x3BA}}\)\(\def\uplambda{\unicode[Times]{x3BB}}\)\(\def\upmu{\unicode[Time...
Comptes Rendus de l'Académie des Sciences - Series IIA - Earth and Planetary Science, 1999
Journal of Shellfish Research, 2008
ABSTRACT growth (as compared with the antero-posterior valve length) in the two clam populations ... more ABSTRACT growth (as compared with the antero-posterior valve length) in the two clam populations showed that growth was negatively affected in the abnormal population. Affected individuals contained more intravalve water than normal individuals. The different growth metrics all indicated that affected clams were less well developed than unaffected clams. The organisms living in association with Venus verrucosa have a negative impact on shell thickness, on shell dry weight and on biomass (as dry flesh). Thin biometric growth study indicates (hat hetero-specific associations stressed the studied affected Clam population and retarted somatic growth. It is suggested that clam emergence. probably caused by adverse conditions. encourages the formation of unfavorable heterotrophic associations by invertebrate species.Monthly monitoring of the clam Venus verrucosa was carried out in the channel of Bizerta Lagoon (Tunisia) from September 2002 to August 2003. Approximately 100 individuals were collected on each occasion from between 7- and 9-m depth. Individual shell sizes (measured as the antero-posterior shell length) varied from 13.7-59 mm. Some specimens showed shell abnormalities that indicated a heterospecific association. The proportion of specimens affected by these abnormalities was high (38%) and a comparison of the relative growth of healthy and abnormal clams was made. The relative growth of shell thickness and weight parameters, were compared with the antero-posterior valve length measurements. We calculated regression equations for annual and seasonal changes in valve length with shell thickness (E/L) and with shell weight (W/L). Annual and seasonal assessments of relartive
Occupational and Environmental Medicine, 1971
323-329. Decompression sickness in caisson workers. An investigation of 55 bridge construction wo... more 323-329. Decompression sickness in caisson workers. An investigation of 55 bridge construction workers is reported. The overall bends rate was 097 %. (The term 'bends' as used in this study is defined in the paper.) Chokes were encountered in 67-27 % of workers. A clinical, haematological, and radiological study was performed. Definite bony changes were found in 43-6% of all workers; 91-6% of these had lesions around the elbow. The presence of dense areas in the neck of the scapula is reported in two cases for the first time. The relatively high haematocrit value is thought to play a part in the pathogenesis of bone infarction through its relation with blood viscosity.
Journal of African Earth Sciences, 2011
... well logs. Taher Zouaghi a , Corresponding Author Contact Information , E-mail The Correspond... more ... well logs. Taher Zouaghi a , Corresponding Author Contact Information , E-mail The Corresponding Author , Issam Ferhi a , b , Mourad Bédir a , Mohamed Ben Youssef a , Mohamed Gasmi b and Mohamed Hédi Inoubli c. a Laboratoire ...
Contemporary Arab Affairs, 2012
This article draws on implications of the Arab Spring so as to elucidate the dynamics that charac... more This article draws on implications of the Arab Spring so as to elucidate the dynamics that characterize its revolutions. The analysis builds upon the results of major public opinion surveys conducted in the Arab world, both immediately before and after the Arab Spring, in order to facilitate the identification of developments that shape the relationship between Arabism and Islamism in the context of mass media, the demographic ‘youth bulge’ and Arab ongoing intellectual debates. The argument advanced here is that the Arab Spring consolidates the view that Arabism and Islamism have maintained their position and hold on public opinion and prevailing attitudes as the primary and inseparable trends of Arab thought. The interaction and shifting relative weights of both trends provide the context for the identity, conceptual outlook and reciprocal framework of contemporary Arabs; and the Arab Spring seems only to confirm the two trends as constituting the essential point of reference and ...
Comparative Clinical Pathology, 2012
This study aimed to compare the sensitivity of different culture methods from three different ana... more This study aimed to compare the sensitivity of different culture methods from three different anatomic sites and to evaluate the sensitivity of polymerase chain reaction (PCR) assay targeting the 16 S ribosomal RNA gene in detection of group B streptococcus (GBS) colonization in pregnant women. From 100 pregnant women at 35-37 weeks of gestation, three cotton swabs were used to obtain vaginal, rectal, and rectovaginal (RV) specimens and plated onto Columbia agar with colistin and nalidixic (CNA), group B streptococcus differential agar (GBSDA), and chromID Strepto B agar (CA), with and without Lim broth enrichment. PCR assay was done on the RV swabs. The overall GBS colonization rate was 29 % by culture and 31 % by PCR. GBS positivity for RV sampling (100 %) was significantly higher than detection on the basis of vaginal sampling (50 %), but not significantly higher than for rectal sampling (82 %). Direct plating of the rectovaginal swab on CNA, GBSDA, and CA resulted in detection of 74, 58, and 100 % of the carriers, respectively, whereas subculturing of Lim broth yielded 65, 59, and 83 % positivity, respectively. Using GBS culture as the "gold standard," the sensitivity of PCR was 100 %, and specificity was 97 %. We found that the inoculation of RV secretions directly onto CA is the most rapid, easy, and sensitive method than that of Lim broth enrichment. Also, we found that group B streptococci can be detected rapidly and reliably by a PCR assay of rectovaginal secretions from pregnant women.
Chemistry of Materials, 2010
This paper describes the preparation of Langmuir-Blodgett (LB) films comprised of an oligomeric p... more This paper describes the preparation of Langmuir-Blodgett (LB) films comprised of an oligomeric phenylene-ethynylene (OPE) derivative, 4-[4-(phenylethynyl)-phenylethynyl] benzoic acid (BPEBA). Analysis of the surface pressure and surface potential vs area per molecule isotherms reveal that good quality monolayer films can be formed at surface pressures of 15 mN/m. The monolayers were transferred onto solid substrates with a Z-type deposition and a transfer ratio of 1. Raman and surface-enhanced Raman spectroscopy (SERS) studies reveal that the films are physisorbed onto silver metal substrates. The morphology of the deposited films was analyzed by means of atomic force microscopy (AFM), revealing the formation of homogeneous layers free of three-dimensional defects. The optical and emissive properties of the LB films were determined, with significant blueshifted absorption spectra indicating the formation of two-dimensional H aggregates in the films. In addition, a significant Stokes shift in the excitation and emission spectra of the films is indicative of a distribution of molecular conformations around the long molecular axis in the solidlike monolayer environment. Scanning tunneling microscopy (STM) studies of single layer BPEBA LB films were performed. The tip-sample distance has been calibrated carefully to obtain I-V curves above the LB film. I-V curves are unexpectedly symmetrical in spite of the asymmetric contacts of the molecule with the tip and the substrate. Single molecule conductance for BPEBA has also been determined and the similarity of these results to I-V data for BPEBA incorporated in LB films indicates that lateral (intermolecular) conductance is negligible for electrical measurements using the STM configuration.
Catalysis Communications, 2001
A series of Ca-de®cient and Co-containing hydroxyapatite samples, noted A r and C x , respectivel... more A series of Ca-de®cient and Co-containing hydroxyapatite samples, noted A r and C x , respectively, where r is the total Ca/P molar ratio (r 1:46±1.62) and x the Co wt%, were prepared by precipitation in aqueous media. The catalytic activities of CoMo/A r and Mo/C x sulphided catalysts have been examined for the S±S bond hydrogenolysis of dimethyldisulphide (DMDS) under relatively mild operating conditions (200°C, 1 atm). The overall activity depends on the Co depositing mode and the hydroxyapatite carrier Ca/P molar ratio. Depositing Co by impregnation on hydroxyapatite samples with low Ca/P molar ratios involves an increase of the catalytic activity until approaching that corresponding to CoMo=Al 2 O 3 catalyst. This can be attributed probably to a better dispersion of the CoMo sulphided catalysts on apatitic carrier with low Ca/P molar ratios. DMDS is selectively reduced to CH 3 SH on the CoMo=A 1;46 sulphided catalyst than on the CoMo=Al 2 O 3 one, even at conversions as higher as 100%.
Australian Journal of Chemistry, 1973
The preparation and some reactions of the N-tosyl derivative of 3-(2?- nitropropenyl)indole (1), ... more The preparation and some reactions of the N-tosyl derivative of 3-(2?- nitropropenyl)indole (1), indole-3-carbaldehyde (2), indole-3- glyoxylamide (3), and 2,3-di-hydrocarbazol-4(1H)-one (7) are described. The N-tosylnitropropenyl derivative (1) was converted into α-methyl-1- tosyltryptamine, and the reaction of 2,3-dihydro-9-tosyl-carbazol-4(1H)-one (7) with ethoxyethynylmagnesium bromide and in the Mannich and Cope-Knoevenagel reactions are described.
8th International Symposium on Parallel Architectures,Algorithms and Networks (ISPAN'05)
Recently, we have proposed ANSWER: AutoNomouS Wireless sEnsor netwoRk as a service platform whose... more Recently, we have proposed ANSWER: AutoNomouS Wireless sEnsor netwoRk as a service platform whose mission is to provide dependable information services to in-situ mobile users while satisfying their quality-of-service (QoS) requirements. Alongside with the stationary tiny sensors, the network employs more powerful mobile devices referred to as aggregation and forwarding nodes (AFNs). ANSWER exploits AFN mobility to support QoS requirements. However, as an AFN moves closer to an event (e.g., a hazardous spill), it may be at risk (e.g., due to potential damage). In this paper, we present a quantitative analysis of the interplay and balance between QoS support and asset safety. We propose a new scheme, called SAFER (for SAFEty-aware Relocation), which pursues relocation of the AFN in order to boost network performance without unnecessarily compromising AFN safety. SAFER uses historical data on detected events and employs an evolutionary neural network to assess the risk involved and predict good quality new position(s).
23rd Biennial Symposium on Communications, 2006
In wireless sensor networks, sensor readings are gathered at a gateway for processing and forward... more In wireless sensor networks, sensor readings are gathered at a gateway for processing and forwarding to a remote commend center. The closeness of the gateway to potentially dangerous events, e.g. fires, exposes it to damage and thus risks making the network dysfunctional. Recently, we have introduced SAFER (safety-aware relocation); a novel approach for protecting the gateway. SAFER strives to relocate
Proceedings of the 2007 international conference on Wireless communications and mobile computing - IWCMC '07, 2007
Abstract Knowledge of node's locations is an essential requirement f... more Abstract Knowledge of node's locations is an essential requirement for many applications of wireless sensor networks. A major problem with multi-hop location discovery is the accumulated error. In this paper, we analyze the effect of reflection errors and present the Multi-hop Relative Location Estimation (MRLE) algorithm that estimates relative node's positions with low error margins. We capture the impact of different parameters on the accuracy of the estimated position and introduce a new metric, called the CLIQUE factor, ...
2010 IEEE Global Telecommunications Conference GLOBECOM 2010, 2010
Adding location to the available information enables a new category of applications. With the con... more Adding location to the available information enables a new category of applications. With the constrained battery on cell phones, energy-efficient localization becomes an important challenge. In this paper we introduce a low-energy calibrationfree localization scheme based on the available internal sensors in many of today's phones. We start by energy profiling the different sensors that can be used for localization. Based on that, we propose GAC: a hybrid GPS/accelerometer/compass scheme that depends mainly on using the low-energy accelerometer and compass sensors and uses the GPS infrequently for synchronization. We implemented our system on Android-enabled cell phones and evaluated it in both highways and intra-city driving environments. Our results show that the proposed hybrid scheme has an exponential saving in energy, with a linear loss in accuracy compared to the GPS accuracy. We also evaluate the effect of the different parameters on the energy-accuracy tradeoff.
IEEE Globecom 2006, 2006
Clustering is a standard approach for achieving efficient and scalable performance in wireless se... more Clustering is a standard approach for achieving efficient and scalable performance in wireless sensor networks. Most of the published clustering algorithms strive to generate the minimum number of disjoint clusters. However, we argue that guaranteeing some degree of overlap among clusters can facilitate many applications, like inter-cluster routing, topology discovery and node localization, recovery from cluster head failure, etc. We formulate the overlapping multi-hop clustering problem as an extension to the k-dominating set problem. Then we propose MOCA; a randomized distributed multi-hop clustering algorithm for organizing the sensors into overlapping clusters. We validate MOCA in a simulated environment and analyze the effect of different parameters, e.g. node density and network connectivity, on its performance. The simulation results demonstrate that MOCA is scalable, introduces low overhead and produces approximately equal-sized clusters.
Urology, 1975
Although urinary bilharziasis (schistosomiasis) is not endemic in the United States, its aftermat... more Although urinary bilharziasis (schistosomiasis) is not endemic in the United States, its aftermath is seen in many patients coming from endemic areas. The aim of this article is to familiarize the readers with what is believed to be representative radiologic manifestations of the bilharzial ureter. Urinary bilharziasis (schistosomiasis) is a parasitic disease endemic in many parts of the world. Egypt has been plagued by this parasite for more than 3,000 years .' The parasite is almost immune to all types of medication ; and in many instances while the patient might have succumbed to a potent drug, the parasites will be found healthy and alive at autopsy examination. Bilharzia affects the bladder and lower ureters principally. The pathologic condition varies from TABLE I. Different pathologic manifestations in 511 patients with bilharzial ureteritis 118 *Only 218 patients underwent eystograms .
International Journal of Colorectal Disease, 2008
Abstract Purpose Anismus is a significant cause of chronic consti-pation. This study came to revi... more Abstract Purpose Anismus is a significant cause of chronic consti-pation. This study came to revive the results of BFB training and BTX-A injection in the treatment of anismus patients. Materials and methods Forty-eight patients with anismus (33 women; mean age 39.6±15.9) were ...
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Papers by Youssef Mohamed