Stochastic Analysis of Non-slotted Aloha in Wireless Ad-Hoc Networks

In this paper we propose two analytically tractable stochastic models of non-slotted Aloha for Mobile Ad-hoc NETworks (MANETs): one model assumes a static pattern of nodes while the other assumes that the pattern of nodes varies over time. Both models feature transmitters randomly located in the Euclidean plane, according to a Poisson point process with the receivers randomly located at a fixed distance from the emitters. We concentrate on the so-called outage scenario, where a successful transmission requires a Signal-to-Interference-and-Noise Ratio (SINR) larger than a given threshold. With Rayleigh fading and the SINR averaged over the duration of the packet transmission, both models lead to closed form expressions for the probability of successful transmission. We show an excellent matching of these results with simulations. Using our models we compare the performances of non-slotted Aloha to previously studied slotted Aloha. We observe that when the path loss is not very strong both models, when appropriately optimized, exhibit similar performance. For stronger path loss non-slotted Aloha performs worse than slotted Aloha, however when the path loss exponent is equal to 4 its density of successfully received packets is still 75% of that in the slotted scheme. This is still much more than the 50% predicted by the well-known analysis where simultaneous transmissions are never successful. Moreover, in any path loss scenario, both schemes exhibit the same energy efficiency.Comment: accepted for IEEE Infocom 201

A Markovian Analysis of IEEE 802.11 Broadcast Transmission Networks with Buffering

The purpose of this paper is to analyze the so-called back-off technique of the IEEE 802.11 protocol in broadcast mode with waiting queues. In contrast to existing models, packets arriving when a station (or node) is in back-off state are not discarded, but are stored in a buffer of infinite capacity. As in previous studies, the key point of our analysis hinges on the assumption that the time on the channel is viewed as a random succession of transmission slots (whose duration corresponds to the length of a packet) and mini-slots during which the back-o? of the station is decremented. These events occur independently, with given probabilities. The state of a node is represented by a two-dimensional Markov chain in discrete-time, formed by the back-off counter and the number of packets at the station. Two models are proposed both of which are shown to cope reasonably well with the physical principles of the protocol. The stabillity (ergodicity) conditions are obtained and interpreted in terms of maximum throughput. Several approximations related to these models are also discussed

Optical determination of the relation between the electron-boson coupling function and the critical temperature in high Tc_c cuprates

We take advantage of the connection between the free carrier optical conductivity and the glue function in the normal state, to reconstruct from the infrared optical conductivity the glue-spectrum of ten different high-Tc cuprates revealing a robust peak in the 50-60 meV range and a broad con- tinuum at higher energies for all measured charge carrier concentrations and temperatures up to 290 K. We observe that the strong coupling formalism accounts fully for the known strong temperature dependence of the optical spectra of the high Tc cuprates, except for strongly underdoped samples. We observe a correlation between the doping trend of the experimental glue spectra and the critical temperature. The data obtained on the overdoped side of the phase diagram conclusively excludes the electron-phonon coupling as the main source of superconducting pairing.Comment: Accepted for publication in Phys. Rev.

CIITA-induced occupation of MHC class II promoters is independent of the cooperative stabilization of the promoter-bound multi-protein complexes

Precise regulation of MHC class II expression plays a crucial role in the control of the immune response. The transactivator CIITA behaves as a master controller of constitutive and inducible MHC class II gene activation, but its exact mechanism of action is not known. Activation of MHC class II promoters requires binding of at least three distinct multi-protein complexes (RFX, X2BP and NF-Y). It is known that the stability of this binding results from cooperative interactions between these proteins. We show here that expression of CIITA in MHC class II- cells triggers occupation of the promoters by these complexes. This observation raised the possibility that the effect of CIITA on promoter occupation is mediated by an effect on the cooperative stabilization of the DNA-bound multi-protein complexes. We show, however, that the presence of CIITA does not affect the stability of the higher-order protein complex formed on DNA by RFX, X2BP and NF-Y. This suggests other mechanisms for CIITA-induced promoter occupancy, such as an effect on chromatin structure leading to increased accessibility of MHC class II promoters. This ability of CIITA to facilitate promoter occupation is undissociable from its transactivation potential. Finally, we conclude that this effect of CIITA is cell-type specific, since expression of CIITA is not required for normal occupation of MHC class II promoters in B lymphocyte

The noradrenergic profile of plasma metanephrine in neuroblastoma patients is reproduced in xenograft mice models and arise from PNMT downregulation.

Metanephrines (MNs; normetanephrine (NMN), metanephrine (MN) and methoxytyramine (MT)) detected in urine or plasma represent the best biomarker for neuroblastoma (NB) diagnosis, however the metabolism of both catecholamine (CAT) and MNs remains enigmatic in NB. Using patient-derived xenograft (PDX) models derived from primary NB cells, we observed that the plasma levels of MNs in NB-PDX-bearing mice were comparable as in patients. Interestingly, murine plasma displayed an elevated fraction of glucuronidated forms of MNs relative to human plasma where sulfonated forms prevail. In tumors, the concentration ranges of MNs and CAT and the expression levels of the main genes involved in catecholamine metabolism were similar between NB-PDX and human NB tissues. Likewise, plasma and intratumoral profiles of individual MNs, with increased levels of MT and NMN relative to MN, were also conserved in mouse models as in patients. We further demonstrated the downregulation of the Phenylethanolamine N-Methyltransferase gene in NB biopsies and in NB-PDX explaining this biochemical phenotype, and giving a rational to the low levels of epinephrine and MN measured in NB affected patients. Thus, our subcutaneous murine NB-PDX models not only reproduce the phenotype of primary NB tumors, but also the metabolism of catecholamine as observed in patients. This may potentially open new avenues in preclinical studies for the follow up of novel therapeutic options for NB through the quantification of plasma MNs

Mechanisms of Surface Antigenic Variation in the Human Pathogenic Fungus <i>Pneumocystis jirovecii</i>.

Microbial pathogens commonly escape the human immune system by varying surface proteins. We investigated the mechanisms used for that purpose by &lt;i&gt;Pneumocystis jirovecii&lt;/i&gt; This uncultivable fungus is an obligate pulmonary pathogen that in immunocompromised individuals causes pneumonia, a major life-threatening infection. Long-read PacBio sequencing was used to assemble a core of subtelomeres of a single &lt;i&gt;P. jirovecii&lt;/i&gt; strain from a bronchoalveolar lavage fluid specimen from a single patient. A total of 113 genes encoding surface proteins were identified, including 28 pseudogenes. These genes formed a subtelomeric gene superfamily, which included five families encoding adhesive glycosylphosphatidylinositol (GPI)-anchored glycoproteins and one family encoding excreted glycoproteins. Numerical analyses suggested that diversification of the glycoproteins relies on mosaic genes created by ectopic recombination and occurs only within each family. DNA motifs suggested that all genes are expressed independently, except those of the family encoding the most abundant surface glycoproteins, which are subject to mutually exclusive expression. PCR analyses showed that exchange of the expressed gene of the latter family occurs frequently, possibly favored by the location of the genes proximal to the telomere because this allows concomitant telomere exchange. Our observations suggest that (i) the &lt;i&gt;P. jirovecii&lt;/i&gt; cell surface is made of a complex mixture of different surface proteins, with a majority of a single isoform of the most abundant glycoprotein, (ii) genetic mosaicism within each family ensures variation of the glycoproteins, and (iii) the strategy of the fungus consists of the continuous production of new subpopulations composed of cells that are antigenically different. &lt;b&gt;IMPORTANCE&lt;/b&gt; &lt;i&gt;Pneumocystis jirovecii&lt;/i&gt; is a fungus causing severe pneumonia in immunocompromised individuals. It is the second most frequent life-threatening invasive fungal infection. We have studied the mechanisms of antigenic variation used by this pathogen to escape the human immune system, a strategy commonly used by pathogenic microorganisms. Using a new DNA sequencing technology generating long reads, we could characterize the highly repetitive gene families encoding the proteins that are present on the cellular surface of this pest. These gene families are localized in the regions close to the ends of all chromosomes, the subtelomeres. Such chromosomal localization was found to favor genetic recombinations between members of each gene family and to allow diversification of these proteins continuously over time. This pathogen seems to use a strategy of antigenic variation consisting of the continuous production of new subpopulations composed of cells that are antigenically different. Such a strategy is unique among human pathogens

NDR: Noise and Dimensionality Reduction of CSI for indoor positioning using deep learning

International audienceDue to the emerging demand for IoT applications, indoor positioning became an invaluable task. We propose a novel lightweight deep learning solution to the indoor positioning problem based on noise and dimensionality reduction of MIMO Channel State Information (CSI). Based on preliminary data analysis, the magnitude of the CSI is selected as the input feature for a Multilayer Perceptron (MLP) neural network. Polynomial regression is then applied to batches of data points to filter noise and reduce input dimensionality by a factor of 14. The MLP’s hyperparameters are empirically tuned to achieve the highest accuracy. The proposed solution is compared with a state-of-the-art method presented by the authors who designed the MIMO antenna that is used to generate the dataset. Our method yields a mean error which is 8 times less than that of its counterpart. We conclude that the arithmetic mean and standard deviation misrepresent the results since the errors follow a log- normal distribution. The mean of the log error distribution of our method translates to a mean error as low as 1.5 cm

A lightweight forwarding strategy for Named Data Networking in low-end IoT

International audienc

A down-to-earth integration of Named Data Networking in the real-world IoT

International audienceThe IEEE802.15.4 wireless technology is one of the enablers of the Internet of Things. It allows constrained devices to communicate with a satisfactory data rate, payload size and distance range, all with reduced energy consumption. To provide IoT devices with a global Internet identity, 6LoWPAN defines the IPv6 adaptation to communicate over IEEE802.15.4. However, this integration still needs additional protocols to support other IoT requirements, which makes the IP stack in IoT devices more complex and therefore shows the limitations of the IP model to support the needs of future Internet. Named Data Networking represents an alternative that can natively support IoT constraints including mobility, security and human readable data names. This paper is a synthesis of an ongoing work that investigates the integration of NDN with IEEE802.15.4 for constrained IoT devices. The proposed design has been implemented in a real-world smart agriculture scenario, and evaluated by simulation focusing on energy consumption and network overhead in comparison to IP-based protocols

Uso racional de água através de mudança de processo

Agência Nacional do Petróleo – ANPFinanciadora de Estudos e Projetos – FINEPA questão envolvendo a escassez de disponibilidade de recursos hídricos em função do aumento de demanda e de seu desperdício inconsequente tem se mostrado como um tema de alcance e interesse globais. De uma forma geral, instrumentos econômicos e mecanismos de comando e controle têm sido utilizados pelo poder público para regulamentar e conscientizar setores da sociedade quanto ao uso racional da água. No meio industrial brasileiro, a institucionalização da cobrança pelo uso da água pressiona pela busca de mecanismos voltados para a redução do consumo de água e da geração de efluentes industriais, por meio de oportunidades de reuso e/ou reciclo de correntes. O surgimento de técnicas mais eficientes e eficazes se faz necessário para otimizar sistemas de uso de água na planta. Neste contexto, a aplicação de métodos sistemáticos orientados para a redução de efluentes aquosos, pode auxiliar na minimização do impacto ambiental, reduzindo os custos com tratamento e descarte de efluentes. Um destes métodos é o Diagrama de Fontes de Água (DFA), procedimento algorítmico heurístico, que orienta a síntese de fluxogramas alternativos com máximo reuso e/ou reciclo de água no processo. É possível identificar gargalos do sistema de reuso, bem como as unidades industriais que demandam qualidades mais restritivas de água. Para tais unidades é utilizada uma metodologia que gera possibilidades para mudanças que levem a uma redução maior do consumo hídrico. Assim, esse trabalho propõe um procedimento que combine o DFA a mudanças de processo, aumentando o reuso. Este procedimento foi aplicado a uma refinaria de petróleo. Dessa forma, foram obtidos resultados para cenários com contaminantes representativos separadamente, considerando cálcio, sílica, amônia, sulfeto e cloreto. Para cada contaminante foram feitos os cenários considerando apenas o DFA e o DFA seguido de mudanças. Em todos os casos, as mudanças alcançaram cenários com melhores resultados, chegando a até 50% na redução de custo de operação em relação ao caso base, que representa cerca de 5 milhões de dólares por ano. No entanto, o caso mais restritivo foi o sulfeto que com mudanças de processo alcançou apenas 400 mil dólares por ano. Portanto, o procedimento proposto apresenta grande potencial para desengargalar redes de transferência de massa, alcançando redução significativa de demanda global de água