Electron Fabry-Perot interferometer with two entangled magnetic impurities

We consider a one-dimensional (1D) wire along which single conduction electrons can propagate in the presence of two spin-1/2 magnetic impurities. The electron may be scattered by each impurity via a contact-exchange interaction and thus a spin-flip generally occurs at each scattering event. Adopting a quantum waveguide theory approach, we derive the stationary states of the system at all orders in the electron-impurity exchange coupling constant. This allows us to investigate electron transmission for arbitrary initial states of the two impurity spins. We show that for suitable electron wave vectors, the triplet and singlet maximally entangled spin states of the impurities can respectively largely inhibit the electron transport or make the wire completely transparent for any electron spin state. In the latter case, a resonance condition can always be found, representing an anomalous behaviour compared to typical decoherence induced by magnetic impurities. We provide an explanation for these phenomena in terms of the Hamiltonian symmetries. Finally, a scheme to generate maximally entangled spin states of the two impurities via electron scattering is proposed.Comment: 19 page

Evaluating the development potential for intermodal transportation centers using the Miami Intermodal Center (MIC)

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Architecture, 1996 [first author]; and, (M.S.)--Massachusetts Institute of Technology, Dept. of Urban Studies, 1996 [second author].Includes bibliographical references (leaves 143-151).by Omar F. del Rio and Donald R. Hackstaff.M.S

Smart Flow Steering Agent for End-to-End Delay Improvement in Software-Defined Networks

لضمان الإستجابة للخطأ والإدارة الموزعة، يتم استخدام البروتوكولات الموزعة كأحد المفاهيم المعمارية الرئيسية التي تتضمنها شبكة الإنترنت. ومع ذلك، يمكن التغلب على عدم الكفاءة وعدم الاستقرار والقصور بمساعدة بنية الشبكات الجديدة التي تسمى الشبكات المعرفة بالبرمجيات SDN. الخاصية الرئيسية لهذه المعمارية هي فصل مستوى التحكم عن مستوى البيانات. إن تقليل التصادم سيؤدي إلى تحسين سرعة الإستجابة وزيادة البيانات المرسلة بصورة صحيحة، لهذا السبب يجب أن يكون هناك توزيع متجانس للحمل المروري عبر مسارات الشبكة المختلفة. تقدم هذه الورقة البحثية أداة توجيه ذكية SFSA لتوجيه تدفق البيانات بناءاً على ظروف الشبكة الحالية. لتحسين الإنتاجية وتقليل زمن الوصول، فإن الخوارزمية المقترحة SFSA تقوم بتوزيع حركة مرور البيانات داخل الشبكة على مسارات مناسبة ، بالإضافة إلى الإشراف على الإرتباطات التشعبية وحمل مسارات نقل البيانات. تم استخدام سيناريو خوارزمية توجيه شجرة الامتداد الدنياMST وأخرى مع خوارزمية التوجيه المعروفة بفتح أقصر مسار أولاً OSPF لتقييم جودة الخوارمية المقترحة SFSA . على سبيل المقارنة ، بالنسبة لخوارزميات التوجيه المذكروة آنفاً ، فقد حققت استراتيجيةSFSA المقترحة انخفاضاً بنسبة 2٪ في معدل ضياع حزم البيانات PDR ، وبنسبة تتراوح بين 15-45٪ في سرعة إستلام البيانات من المصدر إلى الالوجهة النهائية لحزمة البيانات وكذلك انخفاض بنسبة 23 ٪ في زمن رحلة ذهاب وعودة RTT . تم استخدام محاكي Mininet ووحدة التحكم POX لإجراء المحاكاة. ميزة أخرى من SFSA على MST و OSPF هي أن وقت التنفيذ والاسترداد لا يحمل تقلبات. يتقوم أداة التوجيه الذكية المقترحة في هذه الورقة البحثية من فتح أفقاً جديداً لنشر أدوات ذكية جديدة في شبكة SDN تعزز قابلية برمجة الشبكات وإدارتها .To ensure fault tolerance and distributed management, distributed protocols are employed as one of the major architectural concepts underlying the Internet. However, inefficiency, instability and fragility could be potentially overcome with the help of the novel networking architecture called software-defined networking (SDN). The main property of this architecture is the separation of the control and data planes. To reduce congestion and thus improve latency and throughput, there must be homogeneous distribution of the traffic load over the different network paths. This paper presents a smart flow steering agent (SFSA) for data flow routing based on current network conditions. To enhance throughput and minimize latency, the SFSA distributes network traffic to suitable paths, in addition to supervising link and path loads. A scenario with a minimum spanning tree (MST) routing algorithm and another with open shortest path first (OSPF) routing algorithms were employed to assess the SFSA. By comparison, to these two routing algorithms, the suggested SFSA strategy determined a reduction of 2% in packets dropped ratio (PDR), a reduction of 15-45% in end-to-end delay according to the traffic produced, as well as a reduction of 23% in round trip time (RTT). The Mininet emulator and POX controller were employed to conduct the simulation. Another advantage of the SFSA over the MST and OSPF is that its implementation and recovery time do not exhibit fluctuations. The smart flow steering agent will open a new horizon for deploying new smart agents in SDN that enhance network programmability and management

Effect of Static Disorder in an Electron Fabry-Perot Interferometer with Two Quantum Scattering Centers

In a recent paper -- F. Ciccarello \emph{et al.}, New J. Phys. \textbf{8}, 214 (2006) -- we have demonstrated that the electron transmission properties of a one-dimensional (1D) wire with two identical embedded spin-1/2 impurities can be significantly affected by entanglement between the spins of the scattering centers. Such effect is of particular interest in the control of transmission of quantum information in nanostructures and can be used as a detection scheme of maximally entangled states of two localized spins. In this letter, we relax the constraint that the two magnetic impurities are equal and investigate how the main results presented in the above paper are affected by a static disorder in the exchange coupling constants of the impurities. Good robustness against deviation from impurity symmetry is found for both the entanglement dependent transmission and the maximally entangled states generation scheme.Comment: 4 pages, 5 figure

Privacy and Online Social Networks: A Systematic Literature Review of Concerns, Preservation, and Policies

Background: Social media usage is one of the most popular online activities, but with it comes privacy concerns due to how personal data are handled by these social networking sites. Prior literature aimed at identifying users’ privacy concerns as well as user behavior associated with privacy mitigation strategies and policies. However, OSN users continue to divulge private information online and privacy remains an issue. Accordingly, this review aims to present extant research on this topic, and to highlight any potential research gaps. Method: The paper presents a systematic literature review for the period 2006 - 2021, in which 33 full papers that explored privacy concerns in online social networks (OSN), users’ behavior associated with privacy preservation strategies and OSN privacy policies were examined. Results: The findings indicate that users are concerned about their identity being stolen, the disclosure of sensitive information by third-party applications and through data leakage and the degree of control users have over their data. Strategies such as encryption, authentication, and privacy settings configuration, can be used to address users’ concerns. Users generally do not leverage privacy settings available to them, or read the privacy policies, but will opt to share information based on the benefits to be derived from OSNs. Conclusion: OSN users have specific privacy concerns due primarily to the inherent way in which personal data are handled. Different preservation strategies are available to be used by OSN users. Policies are provided to inform users, however, these policies at times are difficult to read and understand, but studies show that there is no direct effect on the behavior of OSN users. Further research is needed to elucidate the correlation between the relative effectiveness of different privacy preservation strategies and the privacy concerns exhibited by users. Extending the research to comparatively assess different social media sites could help with better awareness of the true influence of privacy policies on user behavior

Evidence-based Approach to Establish Space Suit Carbon Dioxide Limits

A literature survey was conducted to assess if published data (evidence) could help inform a space suit carbon dioxide (CO2) limit. The search identified more than 120 documents about human interaction with elevated CO2. Until now, the guiding philosophy has been to drive space suit CO2 as low as reasonably achievable. NASAs EVA Office requested an evidencebased approach to support a new generation of exploration-class extravehicular activity (EVA) space suits. Specific literature data about CO2 are not available for EVA in microgravity because EVA is an operational activity and not a research platform. However, enough data from groundbased research are available to facilitate a consensus of expert opinion on space suit CO2 limits. The compilation of data in this report can answer many but not all concerns about the consequences of hypercapnic exercise in a space suit. Inspired partial pressure of CO2 (PICO2) and not dry-gas partial pressure of CO2 (PCO2) is the appropriate metric for hypercapnic dose to establish space suit CO2 limits. The reduction of inspired gas partial pressures by saturation of the inspired gases with water vapor at 37C is a significant factor under conditions of hypobaric space suit operation. Otherwise healthy EVA astronauts will exhibit wide variability in responses to acute hypercapnia while at rest and during exercise. What is clear from the literature is the absence of prospective (objective) accept or reject criteria for CO2 exposure in general, and no such criteria exist for operating a space suit. There is no absolute Gold Standard for an acceptable acute hypercapnic limit, just a gradual decrease in performance as CO2 increases. Acceptable CO2 exposure limits are occupation, situation (learned or novel tasks), and personspecific. Investigators who measured hypercapnic physiology rarely correlated those changes to neurocognitive symptoms, and those that measured hypercapnic neurocognition rarely correlated those changes with physiology. Some answers about changes in neurocognition and functional EVA performance during hypercapnic exercise in a space suit await new research

Time Averaged Quantum Dynamics and the Validity of the Effective Hamiltonian Model

We develop a technique for finding the dynamical evolution in time of an averaged density matrix. The result is an equation of evolution that includes an Effective Hamiltonian, as well as decoherence terms in Lindblad form. Applying the general equation to harmonic Hamiltonians, we confirm a previous formula for the Effective Hamiltonian together with a new decoherence term which should in general be included, and whose vanishing provides the criteria for validity of the Effective Hamiltonian approach. Finally, we apply the theory to examples of the AC Stark Shift and Three- Level Raman Transitions, recovering a new decoherence effect in the latter.Comment: 7 pages, 2 figure

Transferencia de materia hacia la solución en la extracción de productos bioactivos de vegetales y su degradación en mezclas de solventes

A quantitative analytic evaluation of the extraction of the natural antimalarial drug artemisinin, in wild plants of Artemisia annua L., using mixtures of ethanol 70% (v/v)-water has ben carried out. This study has been performed in order to find a justification of the reduced recovery of that drug in their isolation processes previously reported, not corresponding to the values of its dosage in the fresh plant material. The results of this work could be useful to interpret similar situations in the isolation of plant natural products.Se ha realizado una evaluación analítica cuantitativa de la extracción de la droga antimalárica natural artemisinina, presente en plantas silvestres de Artemisia annua L., utilizando mezclas de etanol 70% (v/v) - agua. El objetivo ha sido encontrar una justificación de la reducida recuperación de esa droga en los procesos de su aislamiento ya indicados en la literatura y que conducen a la obtención de rendimientos que no corresponden con el dosaje inicial de la droga en el material vegetal fresco. Los resultados de este trabajo podrían ser de utilidad para interpretar situaciones análogas en el aislamiento de productos naturales provenientes de vegetales

Outbreak of gastroenteritis caused by Yersinia pestis in Afghanistan.

Plague, which is most often caused by the bite of Yersinia pestis-infected fleas, is a rapidly progressing, serious disease that can be fatal without prompt antibiotic treatment. In late December 2007, an outbreak of acute gastroenteritis occurred in Nimroz Province of southern Afghanistan. Of the 83 probable cases of illness, 17 died (case fatality 20·5%). Being a case was associated with consumption or handling of camel meat (adjusted odds ratio 4·4, 95% confidence interval 2·2-8·8, P<0·001). Molecular testing of patient clinical samples and of tissue from the camel using PCR/electrospray ionization-mass spectrometry revealed DNA signatures consistent with Yersinia pestis. Confirmatory testing using real-time PCR and immunological seroconversion of one of the patients confirmed that the outbreak was caused by plague, with a rare gastrointestinal presentation. The study highlights the challenges of identifying infectious agents in low-resource settings; it is the first reported occurrence of plague in Afghanistan

Implementing quantum gates through scattering between a static and a flying qubit

We investigate whether a two-qubit quantum gate can be implemented in a scattering process involving a flying and a static qubit. To this end, we focus on a paradigmatic setup made out of a mobile particle and a quantum impurity, whose respective spin degrees of freedom couple to each other during a one-dimensional scattering process. Once a condition for the occurrence of quantum gates is derived in terms of spin-dependent transmission coefficients, we show that this can be actually fulfilled through the insertion of an additional narrow potential barrier. An interesting observation is that under resonance conditions the above enables a gate only for isotropic Heisenberg (exchange) interactions and fails for an XY interaction. We show the existence of parameter regimes for which gates able to establish a maximum amount of entanglement can be implemented. The gates are found to be robust to variations of the optimal parameters.Comment: 7 pages, 3 figure