Delay Impact on Stubborn Mining Attack Severity in Imperfect Bitcoin Network

Stubborn mining attack greatly downgrades Bitcoin throughput and also benefits malicious miners (attackers). This paper aims to quantify the impact of block receiving delay on stubborn mining attack severity in imperfect Bitcoin networks. We develop an analytic model and derive formulas of both relative revenue and system throughput, which are applied to study attack severity. Experiment results validate our analysis method and show that imperfect networks favor attackers. The quantitative analysis offers useful insight into stubborn mining attack and then helps the development of countermeasures.Comment: arXiv admin note: text overlap with arXiv:2302.0021

Delay Analysis of GTS Bridging between IEEE 802.15.4 and IEEE 802.11 Networks for Healthcare Applications

We consider interconnection of IEEE 802.15.4 beacon-enabled network cluster with IEEE 802.11b network. This scenario is important in healthcare applications where IEEE 802.15.4 nodes comprise patient's body area network (BAN) and are involved in sensing some health-related data. BAN nodes have very short communication range in order to avoid harming patient's health and save energy. Sensed data needs to be transmitted to an access point in the ward room using wireless technology with higher transmission range and rate such as IEEE 802.11b. We model the interconnected network where IEEE 802.15.4-based BAN operates in guaranteed time slot (GTS) mode, and IEEE 802.11b part of the bridge conveys GTS superframe to the 802.11b access point. We then analyze the network delays. Performance analysis is performed using EKG traffic from continuous telemetry, and we discuss the delays of communication due the increasing number of patients

Preformulation studies in the development of alginate microparticles prepared by spray-drying method

Alginati su prirodni polimeri koji se zbog svojih poželjnih svojstava uvelike koriste u farmaceutskoj industriji. Novija istraživanja biofarmaceutske primjene alginata usmjerena su k razvoju alginatnih terapijskih sustava s modificiranim oslobađanjem djelatne tvari. Sušenje raspršivanjem jedna je od najčešće korištenih metoda u pripravi takvih terapijskih sustava jer optimiranje procesnih i formulacijskih parametara omogućuje dobivanje čestica željenih fizičko-kemijskih i biofarmaceutskih svojstava. Cilj ovog rada bio je provesti fizičko-kemijsku karakterizaciju triju različitih tipova alginata (Manucol® LKX, Protanal® CR 8133 i Protanal® CR 8223) kao ishodnih polimera, i mikročestica pripravljenih sušenjem raspršivanjem polimernih otopina, a u svrhu optimiranja procesa sušenja i svojstava dobivenog suhog produkta. Uz alginate karakteriziran je i polivinilni alkohol PVA 18-88 (PVA) kao polimer koji se može kombinirati s alginatima u izradi mikročestica željenih biofarmaceutskih svojstava. Sušenje raspršivanjem provedeno je na uređaju ProCepT uz upotrebu ultrazvučne sapnice, konusne kolone za sušenje i srednjeg ciklona s padom tlaka od približno 20 mbar, pri brzini peristaltičke pumpe za dovod uzorka 20%, snazi ultrazvučne sapnice 97%, brzini ulaznog zraka za sušenje 0,25 m3/min i temperaturi ulaznog zraka 120 °C za alginate i 150 °C za PVA. Odabrana konfiguracija uređaja te postavke parametara rezultirali su nedovoljnim sušenjem produkta, što je potrebno uzeti u obzir u sljedećim fazama razvoja. Iskorištenja procesa sušenja bila su u rasponu od 24,69 do 55,27%. Sadržaj vlage u alginatnim mikročesticama kretao se između 10,66 i 11,95%, te je odgovarao količini adsorbirane/apsorbirane vlage na ishodne polimere pri temperaturi od 25 °C i relativnoj vlažnosti od 40%. Relativno velik sadržaj vlage alginatnih mikročestica posljedica je nakupljanja atmosferske vlage nakon sušenja raspršivanjem. Sadržaj vlage u PVA mikročesticama iznosio je 2,52%. Sušenje raspršivanjem otopine polimera PVA rezultiralo je njegovom amorfizacijom, dok su alginati bili amorfne strukture i prije sušenja raspršivanjem. Srednji promjer alginatnih mikročestica kretao se uzmeđu 7,9±2,3 μm i 9,3±2,4 μm. U slučaju PVA mikročestica, uočena je bimodalna raspodjela veličina čestica, sa srednjim promjerom od 15,6±8,1 μm. Alginatne mikročestice sferičnog su oblika i uvrnute površine. PVA mikročestice imaju glatku i ravnu površinu, ali su primjećene i one s rupturama i uvrnućima. Rezultati provedenih analiza korisni su za daljnje optimiranje procesa sušenja raspršivanjem i razvoj mikročestica kao terapijskih sustava temeljenih na alginatu.Alginate is a natural polymer that is widely used in pharmaceutical industry due to its favorable properties. Current research is directed towards the development of alginate based controlled-release drug delivery systems. Spray-drying is one of the most widely used methods for the preparation of such drug delivery systems since optimisation of the process and formulation parameters enables the preparation of particles with desirable physico-chemical and biopharmaceutical properties. The aim of this work was to determine physico-chemical properties of three different alginates (Manucol® LKX, Protanal® CR 8133 i Protanal® CR 8223), as well as alginate microparticles prepared by spray-drying of polymer solutions, with the aim to optimise the spray-drying process and the properties of the dry product. Besides alginates, another polymer, polyvinyl alcohol PVA 18-88 (PVA) was characterised since it can be combined with alginates in order to obtain microparticles with desired biopharmaceutical properties. Spray-drying was performed using the ProCepT spray-dryer with the ultrasonic nozzle, standard conical process column and medium cyclone with pressure fall of 20 mbar, at peristaltic pump speed of 20%, ultrasonic nozzle power of 97%, inlet air flow of 0,25 m3/min, inlet air temperature of 120 °C for alginate samples and 150 °C for PVA sample. The spray-dryer configuration and the process parameters employed resulted in insufficient drying of the product, which should be considered in the following stages of the formulation development. Process yield was in range from 24,69 to 55,27%. The moisture content of the spray-dried alginate microparticles was in range from 10,66 to 11,95% and it was consistent with vapour sorption on constitutive polymers at temperature of 25 °C and 40% of relative humidity. Relatively high moisture content of alginate microparticles was a result of the sorption of atmospheric moisture after the spray-drying process. The moisture content in PVA microparticles was 2,52%. Spray-drying of PVA solution resulted in amorphisation of the polymer material while alginates had an amorphous structure even before spray-drying. The mean diameter of alginate microparticles was in the range from 7,9±2,3 μm to 9,3±2,4 μm. For PVA microparticles bimodal size distribution was observed. The mean diametar of PVA microparticles was 15,6±8,1 μm. Alginate microparticles were spherical in shape with buckled surface. Most of PVA microparticles had smooth surface but those with ruptures and pores were also observed. The results of these analyses are useful for the further optimisation of the spray-drying process and the development of alginate-based microparticles as drug delivery systems

Influence of current reuse LNA circuit parameters on its noise figure

A 2.4 GHz low noise amplifier (LNA) with a bias current reuse technique is proposed in this work. To obtain the optimum noise figure (NF) value, dependence of NF on its most influential LNA parameters has been analyzed. Taking into account the LNA design requirements for other figures of merit, values of the circuit parameters are given for the optimum noise figure

CRS-FL: Conditional Random Sampling for Communication-Efficient and Privacy-Preserving Federated Learning

Federated Learning (FL), a privacy-oriented distributed ML paradigm, is being gaining great interest in Internet of Things because of its capability to protect participants data privacy. Studies have been conducted to address challenges existing in standard FL, including communication efficiency and privacy-preserving. But they cannot achieve the goal of making a tradeoff between communication efficiency and model accuracy while guaranteeing privacy. This paper proposes a Conditional Random Sampling (CRS) method and implements it into the standard FL settings (CRS-FL) to tackle the above-mentioned challenges. CRS explores a stochastic coefficient based on Poisson sampling to achieve a higher probability of obtaining zero-gradient unbiasedly, and then decreases the communication overhead effectively without model accuracy degradation. Moreover, we dig out the relaxation Local Differential Privacy (LDP) guarantee conditions of CRS theoretically. Extensive experiment results indicate that (1) in communication efficiency, CRS-FL performs better than the existing methods in metric accuracy per transmission byte without model accuracy reduction in more than 7% sampling ratio (# sampling size / # model size); (2) in privacy-preserving, CRS-FL achieves no accuracy reduction compared with LDP baselines while holding the efficiency, even exceeding them in model accuracy under more sampling ratio conditions

PA-iMFL: Communication-Efficient Privacy Amplification Method against Data Reconstruction Attack in Improved Multi-Layer Federated Learning

Recently, big data has seen explosive growth in the Internet of Things (IoT). Multi-layer FL (MFL) based on cloud-edge-end architecture can promote model training efficiency and model accuracy while preserving IoT data privacy. This paper considers an improved MFL, where edge layer devices own private data and can join the training process. iMFL can improve edge resource utilization and also alleviate the strict requirement of end devices, but suffers from the issues of Data Reconstruction Attack (DRA) and unacceptable communication overhead. This paper aims to address these issues with iMFL. We propose a Privacy Amplification scheme on iMFL (PA-iMFL). Differing from standard MFL, we design privacy operations in end and edge devices after local training, including three sequential components, local differential privacy with Laplace mechanism, privacy amplification subsample, and gradient sign reset. Benefitting from privacy operations, PA-iMFL reduces communication overhead and achieves privacy-preserving. Extensive results demonstrate that against State-Of-The-Art (SOTA) DRAs, PA-iMFL can effectively mitigate private data leakage and reach the same level of protection capability as the SOTA defense model. Moreover, due to adopting privacy operations in edge devices, PA-iMFL promotes up to 2.8 times communication efficiency than the SOTA compression method without compromising model accuracy.Comment: 12 pages, 11 figure

Prisustvo sojeva stafilokoka rezistentnih na meticilin kod studenata Fakulteta veterinarske medicine Univerziteta u Beogradu

Resistance to methicillin in staphylococci is considered to be one of the most dangerous forms of bacterial resistances to antibiotics. Methicillinresistant staphylococci (MRS) are zoonotic agents which cause local and systemic infections in humans and animals, often with a fatal outcome due to the absence of adequate antibiotic therapy. People colonized with strains of MRS are asymptomatic carriers and reservoirs of these strains in human populations. The aim of this research was to determine the prevalence of strains of MRS among clinically healthy students of the Faculty of Veterinary Medicine in Belgrade. The study was conducted on 100 volunteers: 62 males and 38 females. Given that staphylococci are expected to be found in the highest percentage in the nose and on the armpit skin, the swabs were taken from these regions of each person. Blood agar was innoculated immediately on taking the swabs After the incubation and isolation, the staphylococci were identified to species level. Their susceptibility to methicillin was tested in a disk-diffusion test with cefoxitin. All strains which were found to be resistant to cefoxitin were investigated for the presence of mecA gene with PCR. Staphylococci were isolated in 146 out of the 200 swabs taken: there were 79 nose swabs and 67 axillar swabs positive for these bacteria. Seventeen isolates were resistant to cefoxitin and the presence of the mecA gene was confirmed in seven, four of which were taken from the nose and three from the axillary region. The results of this research show that, being 6%, the prevalence of mecA-positive staphylococci in the population of clinically healthy students of veterinary medicine is significant. The percentage of methicillin-resistant staphylococci was higher in nose than in the axillar region of the students.Rezistencija na meticilin kod stafilokoka smatra se jednim od najopasnijih oblika rezistencije bakterija na antibiotike. Sojevi meticilin rezistentnih stafilokoka (MRS) pripadaju zoonotskim agensima i uzročnici su lokalnih i sistemskih infekcija kod ljudi i životinja, često sa fatalnim ishodom zbog nedostatka efikasne terapije. Ljudi kolonizovani sojevima MRS su asimptomatski nosioci i predstavljaju rezervoare ovih sojeva u humanoj populaciji. Cilj ovog istraživanja je bio da se utvrdi prevalencija izolata MRS kod klinički zdravih studenata Fakulteta veterinarske medicine u Beogradu. U istraživanje je bilo uključeno 100 studenata - dobrovoljaca, 62 muškog i 38 ženskog pola. Brisevi su uzimani iz nosa i pazuha zato što su stafilokoke u najvećem procentu zastupljene u tim regijama. Brisevi su odmah zasejavani na krvni agar. Nakon inkubacije i izolacije, izvršena je identifikacija stafilokoka do vrste. Ispitivanje osetljivosti stafilokoka na meticilin izvedeno je primenom disk difuzione metode sa cefoksitinom. Svi sojevi rezistentni na cefoksitin ispitani su na prisustvo mecA gena metodom lančane reakcije polimeraze (PCR). Od ukupno 200 uzetih briseva izolovano je 146 izolata stafilokoka, 79 iz briseva nosa i 67 iz briseva pazušne regije. Kod 17 izolata ustanovljena je rezistencija na cefoksitin, a kod 7 je utvrđeno prisustvo mecA gena. Četiri mecA pozitivna izolata su poticala iz briseva nosa, a 3 sa kože pazušne regije. Utvrđena prevalencija meticilin-rezistentnih stafilokoka kod klinički zdravih studenata Fakulteta veterinarske medicine od 6%, procenjena je kao značajna. Veća učestalost stafilokoka rezistentnih na meticilin ustanovljena je na sluzokoži nosa u odnosu na kožu pazuha

Otkrivanje prisustva PBP2a (Penicillin-binding proteina 2a) i mecA gena kod meticilin rezistentnih Stafilokoka poreklom od životinja

For the purpose of detecting methicillin (oxacillin) resistance in staphylococcal strains, in a number of microbiological laboratories only disc diffusion method with cefoxitin and/or oxacillin discs is used. Besides this method, it is desirable to determine MIC values for cefoxitin and/or oxacillin. After examination by disc diffusion and dilution methods, latex agglutination is used for the detection of PBP2a and PCR is used for the detection of mecA gene. Use of PCR is not possible in a large number of diagnostic laboratories and as method of choice, latex agglutination test for rapid detection of PBP2a is recommended. In this investigation, as confirmatory methods, latex agglutination and PCR were used for strains that were resistant to oxacillin and/or cefoxitin by disc diffusion and broth microdilution methods. In total, 14 strains of coagulase-negative staphylococci originating from clinical specimens of cats, dogs and chicken were examined. Among isolated strains, it was established that the dominating species was Staphylococcus haemolyticus with 11 isolated strains. Other isolated species were Staphylococcus epidermidis, Staphylococcus capitis and Staphylococcus vitulinus, each with one isolated strain. For all 14 strains, oxacillin MIC values ranged from 0.5 μg/mL to >64 μg/mL and cefoxitin MIC values ranged from 1 μg/mL to >256 μg/mL. Positive agglutination reaction by latex agglutination test was recorded in 13 out of 14 strains. The PCR assay for mecA gene was positive in 12 investigated strains.Radi otkrivanja meticilin (oksacilin)-rezistentnih sojeva stafilokoka u većini mikrobioloških laboratorija koristi se najčešće samo disk difuziona metoda uz primenu antibiogram diskova oksacilina i cefoksitina. Pored navedene metode, poželjno je da se utvrde i vrednosti MIC oksacilina i/ili cefoksitina primenom dilucione metode u bujonu ili agaru. Nakon ispitivanja pomenutim metodama za definitivno utvrđivanje pripadnosti soja grupi meticilin rezistentnih stafilokoka, koriste se metoda lateks aglutinacije za utvrđivanje prisustva PBP2a i PCR metoda za detekciju mecA gena. Kako primena metode PCR nije moguća u većini laboratorija koje se bave rutinskom dijagnostikom, kao metoda izbora preporučuje se lateks aglutinacioni test za brzo otkrivanje PBP2a. U ovom ispitivanju primenjeni su lateks aglutinacioni test i PCR metod, kao potvrdne metode za ispitivanje sojeva stafilokoka koji su bili rezistentni na oksacilin i/ili cefoksitin na osnovu rezultata dobijenih disk difuzionom metodom i mikrodilucionom metodom u bujonu. Ukupno je ispitano 14 sojeva koagulaza - negativnih stafilokoka izolovanih iz kliničkih uzoraka poreklom od pasa, mačaka i kokoši. Među izolovanim sojevima, ustanovljeno je da dominira vrsta Staphylococcus haemolyticus sa 11 izolata, a po jedan soj je izolovan od vrsta Staphylococcus epidermidis, Staphylococcus capitis i Staphylococcus vitulinus . Vrednosti MIC oksacilina za 14 sojeva iznosile su od 0.5 mg/mL do >64 mg/mL, a vrednosti MIC cefoksitina iznosile su od 1 mg/mL do >256 mg/mL. Kod 13 od 14 sojeva utvrđena je pozitivna reakcija aglutinacije primenom lateks aglutinacionog testa. Kod 12 ispitivanih sojeva je utvrđeno prisustvo mecA gena PCR metodom