Fairness-Aware Ranking in Search & Recommendation Systems with Application to LinkedIn Talent Search

We present a framework for quantifying and mitigating algorithmic bias in mechanisms designed for ranking individuals, typically used as part of web-scale search and recommendation systems. We first propose complementary measures to quantify bias with respect to protected attributes such as gender and age. We then present algorithms for computing fairness-aware re-ranking of results. For a given search or recommendation task, our algorithms seek to achieve a desired distribution of top ranked results with respect to one or more protected attributes. We show that such a framework can be tailored to achieve fairness criteria such as equality of opportunity and demographic parity depending on the choice of the desired distribution. We evaluate the proposed algorithms via extensive simulations over different parameter choices, and study the effect of fairness-aware ranking on both bias and utility measures. We finally present the online A/B testing results from applying our framework towards representative ranking in LinkedIn Talent Search, and discuss the lessons learned in practice. Our approach resulted in tremendous improvement in the fairness metrics (nearly three fold increase in the number of search queries with representative results) without affecting the business metrics, which paved the way for deployment to 100% of LinkedIn Recruiter users worldwide. Ours is the first large-scale deployed framework for ensuring fairness in the hiring domain, with the potential positive impact for more than 630M LinkedIn members.Comment: This paper has been accepted for publication at ACM KDD 201

Electrochemical study of the repassivation of titanium in different artificial saliva solutions

The passive film presented at the dental implant surfaces can be damaged or eventually destroyed during insertion and implantation into hard tissue due to abrasion/wear with bone or other materials. However, when the wear action stops, the surface will tend to regenerate immediately, and a new passive film will be formed. In such conditions we are in the presence of a tribo-electrochemical phenomenon which comprises the analysis of two different processes and of the synergism effects between them. In fact, the mechanisms of mechanical degradation due to wear might be influenced by the presence of a corrosive environments, but the electrochemical behaviour of the material is likely to be modified by the presence of the mechanical solicitation and by the presence of wear debris and/or the formation of tribolayers. Also, the repassivation kinetics of the tribocorrosion system during or after mechanical damage becomes an important issue to be studied. This work deals with the study of the repassivation of titanium when in contact with artificial saliva solutions, after mechanical damage. Samples were immersed in different kinds of artificial saliva solutions (artificial saliva (AS), AS + citric acid, AS + anodic, cathodic or organic inhibitor). After stabilisation the passive film was mechanically disrupted and the open-circuit potential (OCP) was monitored both during the mechanical damage and until the repassivation was completed. Additionally, and in order to evaluate the quality of the passive film, EIS measurements were performed before and after mechanical disruption of the passive film. The effect of pH variation and of electrolyte composition on the repassivation evolution was also investigated. Considering the evolution of the open circuit potential represented in figure 1 the approximation ln(E) = ln(k) + b*ln(t) was used to study the repassivation evolution with the time. As it can be observed, the open circuit potential achieved before and after the mechanical damage varies, which indicates that the nature of the electrolyte influences the properties of the passive film. As indicated by the b values presented in Table 1, after repassivation, the AS + citric acid is the solution that provides better repassivation evolution with the time. In contrast, the AS + cathodic inhibitor is the solution that provides worst repassivation evolution. However, the EIS results suggests that AS solution is that providing the most stable and thick passive film. The results obtained with the AS + cathodic or + organic solution shows that these solutions do not have a good influence on the film growth

Repassivation of commercially pure Ti in different saliva solutions under tribocorrosion conditions

The surface of dental implants can undergo wear during insertion and implantation into hard tissue, or, in some conditions, during its lifetime. As a consequence, the passive film presented at the implant surface can be damaged or even totally destroyed. However, if the wear action stops the surface might regenerate, giving origin to a new passive film. As all the process occurs in the presence of a chemical aggressive environment, human saliva, the material is under tribocorrosion conditions. It is also possible to introduce the concept of tribo-electrochemistry which may include two main research areas: the tribocorrosion, where the mechanical solicitations in corrosive environments are studied, and the electrochemistry of film free surfaces, where repassivation kinetics is studied after the removal of the protective oxide film on a passive metal. The main aim of this work was to study the repassivation evolution of commercially pure Ti in artificial saliva solutions. Grade 2 commercial pure titanium samples were subjected to a small alternative sliding in a pin-on-plate tribometer against a corundum ball. At the same time, open-circuit potential (OCP) measurements were performed, before, during and after mechanical disruption of the passive film. Also, to obtain a more detailed information on the characteristics of the original and reformed passive film, EIS measurements were done before and after the mechanical damage. All the test were performed in different kinds of artificial saliva solutions (artificial saliva (AS), AS + citric acid, AS + anodic, cathodic or organic inhibitor). Additionally, the effect of pH and electrolyte composition on the repassivation evolution was also investigated. Finally, all samples were characterized using SEM, EDS, and AFM. Surface roughness was also evaluated. Results show that, in some solutions, the open circuit potential, after repassivation, is more noble than that measured before sliding. Also, the repassivation evolution appears to be strongly affected by the electrolyte nature. The AS + citric acid is the solution that provides a better repassivation evolution with the time, however the stability of the passive film takes some time to be acquired. Also, this solution does not provide a very thick film

Influence of the structural, physical and chemical characteristics of titanium surface oxide layers on its tribocorrosion behaviour in contact with an artificial saliva solution

Titanium has been widely used for dental implant applications because their attractive properties such as low Young modulus, good fatigue strength, excellent corrosion resistance and biocompatibility. However it cannot meet all clinical requirements. 1-2 When inserted in the oral environment, dental implants are submitted to a complex degradation phenomena occurring due to the interaction of tribological and corrosive phenomena which can result on its failure. In fact, most of the failures are a result of the combined action of mechanical solicitations (sliding or abrasive wear, erosion, impact, fretting or fatigue processes) and chemical solicitations as a consequence of contact with saliva, cells or bacteria. Consequently, dental implants become part of a tribocorrosion system, and the investigation of the tribocorrosion mechanisms in such systems becomes essential. 3 Recent work has shown that wear resistance of titanium might be improved selectively using the appropriate surface treatment, such as plasma oxidation, which is also often used to enhance the osseointegration process. 4-5 The main aim of this paper is to study the influence of the characteristics of the oxide layers obtained by plasma oxidation on the tribocorrosion behaviour of c.p. Ti intended for the fabrication of dental implants.The plasma oxidation treatment were performed at three different temperatures (300, 450 and 530ºC) and a detailed study of surface topography (Fig. 1), thickness, structure and chemical composition of the oxidized layers was performed. Tribocorrosion experiments were performed using a reciprocating motion pin-on-plate tribometer with an alumina pin as a counterface material in the presence of Fusayama solution. The applied normal force used was 3N, the stroke length 1mm and the displacement frequency was 1Hz. During rubbing the friction coefficient was monitored. Electrochemical techniques were used to follow the evolution of the system during sliding. Each experiment involved an in situ surface cleaning by a cathodic polarization at -900mv during 3 minutes, and after that a potentiostat was used to impose a passive potential to titanium samples. This experiment allows in situ and in real time following of the corrosion kinetics through current measurements. It is important to refer that electrochemical impedance spectroscopy was also used before and after rubbing in order to evaluate the protective character of the oxide film. The influence of the thickness of the oxide layer and of surface roughness on the wear-corrosion behaviour of the material is discussed in detail. Results clearly showed that plasma oxidation treatments have a strong influence on the tribocorrosion behaviour of titanium. Both the corrosion and wear performance of the samples are improved by the increase of the processing temperature. In relation to friction profile no significant differences were found between all samples tested (μ remains between 0.35 and 0.45). Results show that electrochemical techniques yield useful results

Tribocorrosion studies on commercially pure titanium for dental applications

Tribocorrosion refers to a complex degradation of materials occurring due to the interaction between a tribological process and a corrosive environment. From the tribological point of view, the interaction with the material may include sliding or abrasive wear, erosion, impact, fretting or fatigue processes. The environmental solicitation may result from temperature, humidity, liquids or gases in permanent or intermittent contact with the materials. Failure in the metallic part or of the metal/ceramic interfaces existing in dental restorations, such as crowns and bridges, are still relatively frequent. Also, excessive degradation of dental materials is sometimes observed in other dental materials. Most of the failures are due to the simultaneous action of mechanical (wear, fretting and fatigue) and chemical (saliva) solicitations. As a consequence, the investigation of the tribocorrosion mechanisms in such systems becomes essential. Regarding this aspect, in last years particular focus is being given to the exploitation of electrochemical methods as a tool for the investigation of the combined corrosion-wear degradation of the materials. Also, it is known that the mechanical contact geometry is of crucial importance regarding the degradation behaviour. In this work the tribocorrosion behaviour of commercially pure titanium in contact with artificial saliva solutions was investigated. Tests were conducted in a reciprocating sliding geometry with movement amplitudes varying from 200 m (fretting) up to 6 mm (wear), and normal loads between 2 and 10 N. The electrochemical noise technique was used in order to follow the evolution of both the corrosion current and of the open circuit potential of the system during the wear tests. The pH of the artificial saliva solution was varied between 4 and 7. Results show that the behaviour of the material is strongly influenced by the pH of the solution. In fact, acidification of the solution improves the electrochemical response of the material, in particular the repassivation kinetics after sliding, in all the test conditions used in this work. However, the characteristics of the passive film formed on the material surface appear to be less protective than that formed at neutral pH. Also, an abnormal amount of titanium is removed from the material at low pH, when the normal load applied during the wear test is increased

Characterizing a Mini Gamma Detector

There are several types of gamma radiation detectors, which have different characteristics depending on its use. We designed and instrumented a gamma detector for low energies of a small and portable size to obtain spectrum from radioactive sources and from that analyze each spectrum. This instrument basically consists of a scintillator crystal coupled to a SiPM this in turn coupled to a PCB card designed with capacitors and resistors for a better signal, a voltage source of 29 volts. For signal acquisition the system must be connected to an oscilloscope this in turn is controlled by a script developed in Python. For the calibration radioactive isotopes with the same dimensions were used, caesium-137 (Cs-137), cobalto-60 (Co-60), sodium-22 (Na-22) and manganese-54 (Mn-54) as gamma ray emission

Wear and corrosion of titanium in oral simulating environments

The oral cavity can be considered as an aggressive environment to restorative materials considering that several acidic substances can be retained in the saliva and biofilms as well as loads from mastication and abrasive particles take place in the wear of oral surfaces. The objective of this work is to investigate the in-vitro corrosion and wear in fluoridated artificial saliva and in presence of biofilms. Electrochemical tests of titanium surfaces were performed in artificial saliva containing different fluoride concentrations at 37 oC. Another group of titanium surfaces were prepared to the growth of oral mixed biofilms for 9 days in a specific culture medium. Then, electrochemical tests were carried out with titanium surfaces covered with biofilms in artificial saliva without fluorides. After that, wear sliding tests were performed in the same mediums using a tribometer equipped with a test viewer software. Also, electrochemical measurements were carried during the wear sliding tests. After corrosion-wear tests, worn and unworn surfaces were analyzed by AFM and SEM. A localized corrosion of titanium was only noticed in high fluoride concentration. Therefore, there was a decrease of the corrosion resistance of titanium when the fluoride concentration was increased. Moreover, the presence of biofilms affected harmfully the corrosion resistance of titanium probably due to acids release from the biofilms. However, the wear was decreased when low loads were applied on the biofilms.Fundação para a Ciência e a Tecnologia (FCT) - PTDC/CTM/67500/2006Programa Alban - Bolsas de Alto Nível da União Europeia para a América Latina - E06D103407BRFlemish Science Foundation. Scientific Research Community on Surface Modification of Material

Effect of oral biofilms on the biotribocorrosion of titanium

The oral cavity is a complex environment where corrosive substances from dietary, human saliva and oral biofilms may accumulate in retentive areas of implant-supported prostheses promoting a corrosion of their surfaces. On the other side, during mastication, micro-movements may occur in artificial joints causing a relative contact motion between surfaces. Both processes result in a tribocorrosion system. The objective of this work is to investigate the in-vitro tribocorrosion behavior of titanium covered by biofilms and immersed in artificial saliva. Reciprocating sliding wear tests coupled with electrochemical techniques were performed at 25 o C on titanium samples covered or not with biofilms. Mixed biofilms of Candida albicans and Streptococcus mutans were grown at 37 oC on titanium surfaces for 9 days in Tryptic Soy Broth medium, containing mucin, yeast extract, peptone and sucrose. The open-circuit potential (OCP) was measured until stabilization in artificial saliva. After that, electrochemical impedance spectroscopy (EIS) measurements were carried out at open circuit potential. Subsequently, sliding tests were performed at normal loads of 0.1, 0.2 and 3 N, at a sliding frequency of 1 Hz, and linear displacement amplitudes of 0.5 and 2 mm using a tribometer equipped with a test viewer software. During the sliding tests, the OCP was constantly monitored. At the end of the sliding test, the OCP was further monitored until stabilization, and another series of EIS measurements was made. Worn and unworn surfaces were inspected by SEM. The detachment of the biofilms was not noticed when low loads were applied, and biofilms appear to have some lubricating effect. However, it was found that acidic substances released from Streptococcus mutans and external substances accumulated into the biofilm might corrode surfaces located below and around the biofilms. At a normal load of 3 N, the biofilms were removed from the contact region by the sliding action, and it was observed that the repassivation rate of titanium covered with biofilms was lower than without biofilms.Fundação para a Ciência e a Tecnologia (FCT)ALBANFlemish Science Foundation. Scientific Research Community on Surface Modification of MaterialsPrograma Alban - Bolsas de Alto Nível da União Europeia para a América Latin

Study of CT Images Processing with the Implementation of MLEM Algorithm using CUDA on NVIDIA’S GPU Framework

In medicine, the acquisition process in Computed Tomography Images (CT) is obtained by a reconstruction algorithm. The classical method for image reconstruction is the Filtered Back Projection (FBP). This method is fast and simple but does not use any statistical information about the measurements. The appearance of artifacts and its low spatial resolution in reconstructed images must be considered. Furthermore, the FBP requires of optimal conditions of the projections and complete sets of data. In this paper a methodology to accelerate acquisition process for CT based on the Maximum Likelihood Estimation Method (MLEM) algorithm is presented. This statistical iterative reconstruction algorithm uses a GPU Programming Paradigms and was compared with sequential algorithms in which the reconstruction time was reduced by up to 3 orders of magnitude while preserving image quality. Furthermore, they showed a good performance when compared with reconstruction methods provided by commercial software. The system, which would consist exclusively of a commercial laptop and GPU could be used as a fast, portable, simple and cheap image reconstruction platform in the future