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Biological age uses biophysiological information to capture a person's age-related risk of adverse outcomes. MetaboAge and MetaboHealth are metabolomics-based biomarkers of biological age trained on chronological age and mortality risk, respectively. Lifestyle factors contribute to the extent chronological and biological age differ. The association of lifestyle factors with MetaboAge and MetaboHealth, potential sex differences in these associations, and MetaboAge's and MetaboHealth's sensitivity to lifestyle changes have not been studied yet. Linear regression analyses and mixed-effect models were used to examine the cross-sectional and longitudinal associations of scaled lifestyle factors with scaled MetaboAge and MetaboHealth in 24,332 middle-aged participants from the Doetinchem Cohort Study, Rotterdam Study, and UK Biobank. Random-effect meta-analyses were performed across cohorts. Repeated metabolomics measurements had a ten-year interval in the Doetinchem Cohort Study and a five-year interval in the UK Biobank. In the first study incorporating longitudinal information on MetaboAge and MetaboHealth, we demonstrate associations between current smoking, sleeping ≥8â¯hours/day, higher BMI, and larger waist circumference were associated with higher MetaboHealth, the latter two also with higher MetaboAge. Furthermore, adhering to the dietary and physical activity guidelines were inversely associated with MetaboHealth. Lastly, we observed sex differences in the associations between alcohol use and MetaboHealth.
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Envelhecimento , Biomarcadores , Estilo de Vida , Humanos , Masculino , Feminino , Biomarcadores/sangue , Biomarcadores/metabolismo , Envelhecimento/metabolismo , Envelhecimento/fisiologia , Pessoa de Meia-Idade , Estudos Transversais , Estudos Longitudinais , Estudos Prospectivos , Metabolômica/métodos , Idoso , Exercício Físico/fisiologiaRESUMO
The present study was conducted as the first molecular detection of Anaplasma species in tick samples based on the sequencing of major surface proteins 4 (msp4) gene fragments in different parts of Iran. A total of 130 tick specimens were collected from Hormozgan, Lorestan, and Guilan, Iran, within 2015 to 2017. Hyalomma asiaticum, Hyalomma dromedarii, Rhipicephalus sanguineus, and Rhipicephalus (Boophilus) species were identified in different geographical regions. An amplicon of 464-bp msp4 of Anaplasma was amplified using polymerase chain reaction in various tick species. Three sequences, including one Anaplasma marginale from R. (Boophilus) species and two Anaplasma ovis from Rhipicephalus sanguineus, were obtained after sequencing. It is concluded that bovine and ovine anaplasmosis agents are present in tick samples in Iran. The use of the gene families of six major surface proteins for the detection of various Anaplasma species is recommended.
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Anaplasma marginale , Anaplasma ovis , Ixodidae , Animais , Anaplasma marginale/isolamento & purificação , Anaplasma ovis/isolamento & purificação , Irã (Geográfico) , Ixodidae/microbiologia , Reação em Cadeia da Polimerase , Rhipicephalus/microbiologia , Rhipicephalus sanguineus/microbiologiaRESUMO
Clinically approved neural stimulators are limited by battery requirements, as well as by their large size compared with the stimulation targets. Here, we describe a wireless, leadless and battery-free implantable neural stimulator that is 1.7 mm3 and that incorporates a piezoceramic transducer, an energy-storage capacitor and an integrated circuit. An ultrasonic link and a hand-held external transceiver provide the stimulator with power and bidirectional communication. The stimulation protocols were wirelessly encoded on the fly, reducing power consumption and on-chip memory, and enabling protocol complexity with a high temporal resolution and low-latency feedback. Uplink data indicating whether stimulation occurs are encoded by the stimulator through backscatter modulation and are demodulated at the external transceiver. When embedded in ex vivo porcine tissue, the integrated circuit efficiently harvested ultrasonic power, decoded downlink data for the stimulation parameters and generated current-controlled stimulation pulses. When cuff-mounted and acutely implanted onto the sciatic nerve of anaesthetized rats, the device conferred repeatable stimulation across a range of physiological responses. The miniaturized neural stimulator may facilitate closed-loop neurostimulation for therapeutic interventions.
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Neuroestimuladores Implantáveis , Tecnologia sem Fio , Animais , Fontes de Energia Elétrica , Desenho de Equipamento , Ratos , Nervo Isquiático/fisiologia , Processamento de Sinais Assistido por Computador , UltrassomRESUMO
INTRODUCTION: Influenza is one of the main public health problems and health care personnels (HCPs) are one of the at-risk groups for this infection. The goal of the current study was to identify the beliefs and attitudes of the Iranian HCPs about influenza and the influenza vaccine. METHODS: This cross-sectional study was performed in a general hospital in Tehran, Iran from January to June 2016. A total of 418 questionnaires were distributed among the HCPs. The Chi2 test, linear regression and one-way ANOVA were used for data analysis, α: 0.05 was considered as a statistically significant level. All analyses were performed using the SPSS19 software. RESULTS: The influenza vaccination coverage was 57.7%; the highest vaccine rate belongs to the allied health professionals (68.2%). Two main causes for avoiding the influenza vaccination were; the "fear of vaccine adverse effects" and the "uncertainty about the vaccine effectiveness". The linear regression analysis identified that the physicians had the highest belief score, followed by the nurses and the allied health professionals (p < 0.001). CONCLUSIONS: Educational planning on influenza and influenza vaccination is necessary to improve the vaccination coverage and to reduce the influenza mortality and morbidity in susceptible patients.
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Pessoal Técnico de Saúde , Atitude do Pessoal de Saúde , Vacinas contra Influenza/uso terapêutico , Influenza Humana/prevenção & controle , Enfermeiras e Enfermeiros , Médicos , Cobertura Vacinal , Adulto , Estudos Transversais , Feminino , Hospitais Gerais , Humanos , Irã (Geográfico) , Modelos Lineares , Masculino , Pessoa de Meia-Idade , Adulto JovemRESUMO
In this study, nanoporous titanate (NT) nanoparticle synthesized by the solvothermal method was used to modify polyamide layer of thin film composite membranes with the aim of improving membrane resistances against organic and inorganic fouling. Thin film nanocomposite membranes (NMs) were synthesized by adding mNTs (modified nanoparticles) into polyamide selective layer followed by characterization using different analytical instruments. The results of XPS and XRD confirmed the presence of mNTs in the polyamide layer of NMs, while FESEM, AFM, zeta potential and contact angle measurement further supported the changes in physical and chemical properties of the membrane surface upon mNTs incorporation. Results of fouling showed that NM1 (the membrane incorporated with 0.01w/v% mNTs) always demonstrated lower degree of flux decline compared to the control membrane when membranes were tested with organic, inorganic and multicomponent synthesized water, brackish water or seawater. Besides showing greater antifouling resistance, the NM also displayed significantly higher water flux compared to the control M membrane. The findings of this work confirmed the positive impact of mNTs in improving the properties of NM with respect to fouling mitigation and flux improvement.
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Membranas Artificiais , Nanocompostos/química , Nylons/química , Titânio/química , PorosidadeRESUMO
BACKGROUND: Hypospadias is one of the most common forms of congenital malformation of the male external genitalia worldwide. The ratio in the Iranian population is one in 250 live male births. The conversion of testosterone to dihydrotestosterone (DHT) in the presence of steroid 5α-reductase 2, which is encoded by SRD5A2 gene, plays an important role in the normal development of the male reproductive system. METHODS: We examined whether SRD5A2 gene mutations (V89L and A49T polymorphisms) are associated with the risk of hypospadias in the Iranian population. We performed exons sequencing for SRD5A2 gene in 109 hypospadias patients. RESULTS: We identified two new mutations in the subgroups of affected cases: including a substitution of the nucleotide T > A in the codon 73 [c.219T > A (p.Leu73_Ser74insHisPro)] and an insertion of an extra A nucleotide in the codon 77 [c.229insA* (p.Gly77*)]. Additionally, we performed PCR-RFLP for the two identified polymorphisms and revealed that V89L [OR = 5.8, 95% CI (3.8-8.8), p value < 0.001] and A49T [OR = 10.16, 95% CI (3.94-26.25), p value < 0.001] are significantly associated with hypospadias occurrence in patients. Our haplotype analysis further indicated that the Leu-Ala haplotype increases risk of hypospadias; conversely, the Val-Ala haplotype decreases the risk of hypospadias in the studied patients. CONCLUSIONS: This study demonstrates that polymorphisms in the SRD5A2 gene could be considered as a risk factor for hypospadias disease emergence.
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3-Oxo-5-alfa-Esteroide 4-Desidrogenase/genética , Hipospadia/epidemiologia , Hipospadia/genética , Proteínas de Membrana/genética , Mutação/genética , Estudos de Casos e Controles , Feminino , Predisposição Genética para Doença , Genótipo , Haplótipos , Humanos , Irã (Geográfico)/epidemiologia , Masculino , Prevalência , Fatores de Risco , Testosterona/sangueRESUMO
In a tokamak with a toroidal electric field, electrons that exceed the critical velocity are freely accelerated and can reach very high energies. These so-called `runaway electrons' can cause severe damage to the vacuum vessel and are a dangerous source of hard X-rays. Here the effect of toroidal electric and magnetic field changes on the characteristics of runaway electrons is reported. A possible technique for runaways diagnosis is the detection of hard X-ray radiation; for this purpose, a scintillator (NaI) was used. Because of the high loop voltage at the beginning of a plasma, this investigation was carried out on toroidal electric field changes in the first 5â ms interval from the beginning of the plasma. In addition, the toroidal magnetic field was monitored for the whole discharge time. The results indicate that with increasing toroidal electric field the mean energy of runaway electrons rises, and also an increase in the toroidal magnetic field can result in a decrease in intensity of magnetohydrodynamic oscillations which means that for both conditions more of these high-energy electrons will be generated.
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Elétrons , Raios XRESUMO
In this research, novel ultrafiltration nanocomposite membranes were prepared by incorporating self-synthesized nanoporous titanium dioxide (NTiO2) nanoparticles into polysulfone. The surface of the nanoparticle was treated with a silane-based modifier to improve its distribution in the host polymer. Atomic-force microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, Brunauer-Emmett-Teller, transmission electron microscopy, energy-dispersive x-ray spectroscopy, porosity and contact angle tests were conducted to characterize the properties of the particles as well as the fabricated nanocomposite membranes. The effects of the nanoparticle incorporation were evaluated by conducting ultrafiltration experiments. It was reported that the membrane pure water flux was increased with increasing NTiO2 loading owing to the high porosity of the nanoparticles embedded and/or formation of enlarged pores upon addition of them. The antifouling capacity of the membranes was also tested by ultrafiltration of bovine serum albumin fouling solution. It was found that both water flux and antifouling capacity tended to reach desired level if the NTiO2 added was at optimized loading.
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BACKGROUND & OBJECTIVES: Leishmaniasis is an endemic parasitic disease reported sporadically throughout Iran. Golestan province is one of the 17 zoonotic cutaneous leishmaniasis (ZCL) foci. In this study, ecoepidemiological characteristics of ZCL were investigated in Gonbad-e Kavus County, Golestan province of Iran. METHODS: This cross-sectional study was carried out in three endemic villages and one ZCL-free village by exploiting a stratified random sampling methodology in 2013. To understand particular time-allocation and activity patterns, sandflies were entrapped twice per month using sticky traps from May to October 2013. Records of daily maximum and minimum temperatures (°C) obtained from the meteorological station were used to calculate accumulated degree days (ADD) for Phlebotomus papatasi sandflies using an online software, viz. degree-day calculator, available from the website of Integrated Pest Management, University of California. The computational ADD and expected stage appearance for P. papatasi sandflies were evaluated along with the phenological events. Human infection indices were investigated in the study areas as well. RESULTS: In the entomological survey, a total of 13 different sandfly species were identified. Sergentomyia sintoni (66.8%) and P. papatasi (20%) were observed to be the most dominant species. Monthly activity of the different species of sandflies started from early May to mid-October, with two peaks observed in early July and mid- September, and the peak of hourly activity occurred at night (1900-2000 hrs). According to the phenological study, population dynamics of P. papatasi was completely in agreement with ADD required for the various stages of their growth. Epidemiologically, the highest incidence of ZCL was observed in the age group of 30-34 yr (29.4%). INTERPRETATION & CONCLUSION: Higher incidence of the disease was seen in the northern and the northeastern parts of the province bordered by Turkmenistan. The most effective alternative for controlling the disease in this hypoendemic focus is health education regarding personal protection from infected P. papatasi. The long-term studies are imperative for better understanding and estimation of the factors affecting ZCL transmission in the endemic areas.
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Leishmaniose Cutânea/epidemiologia , Psychodidae/crescimento & desenvolvimento , Zoonoses/epidemiologia , Adolescente , Adulto , Fatores Etários , Idoso , Idoso de 80 Anos ou mais , Animais , Criança , Pré-Escolar , Estudos Transversais , Feminino , Humanos , Incidência , Lactente , Recém-Nascido , Insetos Vetores , Irã (Geográfico)/epidemiologia , Masculino , Pessoa de Meia-Idade , Psychodidae/classificação , Temperatura , Topografia Médica , Adulto JovemRESUMO
In the current study, the impact of self-synthesized nanoporous titanium oxide (NT) on the morphology, performance and fouling of a polyamide (PA) thin-film composite (TFC) membrane was investigated when the membrane was applied for engineering osmosis (EO). The nanoporous structure and the spindle-like shape of NT were revealed through transmission electron microscopy (TEM), while the AATPS modification of NT was verified by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. The results of x-ray photoelectron spectroscopy (XPS) and x-ray diffraction (XRD) confirmed the presence of modified NT (mNT) in the PA dense active layer of the TFC membrane. The outgrowth of the 'leaf-like' structure, upon mNT loading, at the surface of the PA layer was observed by field-emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The TFC membrane prepared with 0.05 wt% mNT loading in the organic phase showed the water flux of 26.4 l m(-2) h(-1) when tested in the forward osmosis (FO) mode using 0.5M and 10 mM NaCl solution as the draw and feed solution, respectively. Moreover, the TFC-mNT membrane also demonstrated an intensified antifouling property against organic foulant during FO application and it was possible to retrieve the initial water flux almost completely with a simple water-rinsing process.
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PURPOSE: Accumulating evidence indicates that intrauterine evolution disturbance can contribute to myocardial ischemia reperfusion (IR) injury; in addition, thyroid hormones (THs) have a crucial role in the development of different systems during fetal life. The aim of this study was to determine the effect of TH deficiency during fetal life on tolerance of isolated heart to ischemia during adulthood in both genders. METHODS: Hypothyroidism was induced in pregnant Wistar rats by administrating 0.025 % 6-propyl-2-thiouracil in drinking water throughout pregnancy. Offspring of rats with maternal hypothyroidism (MH) and control groups were tested in adulthood. Isolated hearts were perfused with Langendorff setup and exposed to 30 min of ischemia, followed by 45 min of reperfusion. Baseline values of the left ventricular end-diastolic pressure (LVEDP), left ventricular developed pressure (LVDP), heart rate (HR), and peak rates of positive and negative changes in left ventricular pressure (±dp/dt) were recorded. RESULTS: In the MH groups the baseline levels of LVDP (male: 23 %, female: 33 %), HR (male: 31 %, female: 26 %), and ±dp/dt were significantly (p < 0.01) lower, compared to controls. After ischemia, hearts from male rats with MH had less tolerance to IR injury as assessed in terms of reductions in recovery of hemodynamic parameters compared to controls, while in female rats there were no significant differences between MH and controls. CONCLUSIONS: MH decreases hemodynamic parameters in the heart of both male and female offspring in adulthood; in addition, hearts of male rats with MH show less tolerance to ischemia, compared to those of females.
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Frequência Cardíaca/fisiologia , Hipotireoidismo/sangue , Traumatismo por Reperfusão Miocárdica/sangue , Efeitos Tardios da Exposição Pré-Natal/sangue , Caracteres Sexuais , Hormônios Tireóideos/sangue , Animais , Feminino , Coração/fisiologia , Hipotireoidismo/complicações , Hipotireoidismo/patologia , Masculino , Traumatismo por Reperfusão Miocárdica/etiologia , Traumatismo por Reperfusão Miocárdica/patologia , Gravidez , Efeitos Tardios da Exposição Pré-Natal/patologia , Ratos , Ratos WistarRESUMO
Plum (Prunus domestica) and peach (P. persica) are widely grown, often in alternate rows with citrus, in the Mazandaran Province of Iran. In June 2011, a dry fruit rot of plum was observed in several production regions in Mazandaran Province (35°47'N, 50°34'E). Initial symptoms at pit-hardening stage appeared as dark brown, circular, necrotic spots from 2 to 5 cm in diameter. They later developed into a dry fruit rot. Severe symptoms occurred during June and July when warm weather (temperature around 28°C) and high relative humidity (RH) (>85%) were present. Marketable yield losses reached 50% to almost 100% in many orchards. To isolate the causal organism, symptomatic fruits were surface disinfested for 1 min in 0.5% active chlorine, washed thoroughly with sterile distilled water, and segments were plated on potato dextrose agar (PDA) amended with 50 mg/liter of streptomycin sulfate and incubated at 25°C for 3 days. The fungus Hyphodermella rosae (Bresadola) Nakasone was consistently isolated (37 isolates from 79 samples) and identified on the basis of morphological characteristics on PDA. Basidiomata were effuse, resupinate, 15 × 10 mm, crustaceous, tubercules small with apical bristles, and light orange to grayish orange. Subhymenium was up to 30 µm thick, composed of vertically arranged, short-celled, nonagglutinated hyphae; subhymenial hyphae were 3 to 4 µm in diameter. Basidiospores were ellipsoid, 7.5 to 8.5 × 4.5 to 5.5 µm (100 determination), and their cell walls were thin, hyaline, and smooth (1). Genomic DNA was extracted from mycelium with a DNA extraction kit (Qiagen, Hilden, Germany) according to the manufacturer's directions and grown on potato dextrose broth for 4 days at 28°C. The rDNA region was amplified with the primers ITS4 (5'-TCCTCCGCTTATTGATATGC-3') and ITS5 (5'- GGAAGTAAAAGTCGTAACAA-3') (4) and the PCR product was sequenced. Nucleotide BLAST analysis of the amplified 627-bp fragment confirmed a 99% similarity with the sequence of H. rosae (GenBank Accession No. JN593086). A pathogenicity test was conducted with isolate MA4099 by placing 5-day-old mycelial plugs grown on PDA at the surface of healthy fruit (n = 6) incubated under >85% RH at 25°C for at least 4 days until the appearance of symptoms, which were similar to those displayed under orchard conditions. Control fruits, inoculated with blocks of PDA plugs, remained intact and symptomless. Reisolation from inoculated fruit samples consistently yielded the inoculated fungus, completing Koch's postulates. The genus Hyphodermella has been reported to be causing wood rot on apricot (2) and sweet and sour cherry (3). To our knowledge, this is the first report of H. rosae causing dry fruit rot on a stone fruit species in the world. References: (1) K. K. Nakasone. Mycologie, 29:231, 2008. (2) J. M. Ogawa et al. Diseases of Apricot (Prunus armeniaca L.). The American Phytopathological Society, St. Paul, MN, 2003. (3) J. K. Uyemoto et al. Diseases of Sweet Cherry (Prunus avium L.) and Sour Cherry (P. cerasus L.). IS-MPMInet, http://www.ismpminet.org/resources/common/comment/cherry.asp , accessed June 2012. (4) T. J. White et al. Page: 315 in: PCR Protocols: A Guide to Methods and Application. M.A. Innis et al., eds. Academic Press, San Diego, CA, 1990.
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Obesity often coexists with low calcium intake and vitamin D insufficiency. There is emerging evidence of a role for these nutrients in the regulation of body weight. However, it is unclear whether increasing intakes of calcium and/or vitamin D during energy restriction, is a better strategy for weight and fat loss. We searched the literature from 2000 to date for randomized controlled trials (RCTs) on weight loss that had increased calcium or vitamin D per se, or in combination. Primary and secondary studies were included for this analysis. A total of 15 RCTs on calcium with or without vitamin D and seven on vitamin D alone met our criteria. Two studies reported that supplemental calcium significantly increased fat loss during caloric restriction by 1.8 and 2.2 kg, three found differences between 1 and 3.5 kg but were statistically nonsignificant, while nine trials were equivocal (±0.7 kg). The data on vitamin D supplementation during weight loss were too few to make firm conclusions. Current evidence from RCTs did not consistently support the contention that calcium and vitamin D accelerated weight or fat loss in obesity. There were studies that favoured the hypothesis but lacked the statistical power. There is a need for RCTs to examine the influence of vitamin D on body fat.
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Cálcio da Dieta/uso terapêutico , Suplementos Nutricionais , Obesidade/tratamento farmacológico , Vitamina D/uso terapêutico , Vitaminas/uso terapêutico , Tecido Adiposo/efeitos dos fármacos , Humanos , Ensaios Clínicos Controlados Aleatórios como Assunto , Redução de PesoRESUMO
The depth of anesthesia quantification has been one of the most research interests in the field of EEG signal processing and nonlinear dynamical analysis has emerged as a novel method for the study of complex systems in the past few decades. In this investigation we use the concept of nonlinear time series analysis techniques to reconstruct the attractor of anesthesia from EEG signal which have been obtained from different hypnotic states during surgery to give a characterization of the dimensional complexity of EEG by Correlation Dimension estimation. The dimension of the anesthesia strange attractor can be thought of as a measure of the degrees of freedom or the ;complexity' of the dynamics at different hypnotic levels. The results imply that for awaked state the correlation dimension is high, On the other hand, for light, moderate and deep hypnotic states these values decrease respectively; which means for anesthetized situation we expect lower correlation dimension.
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Anestesia , Eletroencefalografia , Algoritmos , HumanosRESUMO
The depth of anesthesia estimation has been one of the most research interests in the field of EEG signal processing in recent decades. In this paper we present a new methodology to quantify the depth of anesthesia by quantifying the dynamic fluctuation of the EEG signal. Extraction of useful information about the nonlinear dynamic of the brain during anesthesia has been proposed with the optimum Fractal Scaling Exponent. This optimum solution is based on the best box sizes in the Detrended Fluctuation Analysis (DFA) algorithm which have meaningful changes at different depth of anesthesia. The Fractal Scaling Exponent (FSE) Index as a new criterion has been proposed. The experimental results confirm that our new Index can clearly discriminate between aware to moderate and deep anesthesia levels. Moreover, it significantly reduces the computational complexity and results in a faster reaction to the transients in patients' consciousness levels in relations with the other algorithms.
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Anestesia , Eletroencefalografia/métodos , Fractais , Algoritmos , Anestesiologia/métodos , Anestésicos/uso terapêutico , Encéfalo/patologia , Eletroencefalografia/instrumentação , Humanos , Modelos Estatísticos , Modelos Teóricos , Dinâmica não Linear , Processamento de Sinais Assistido por ComputadorRESUMO
It is shown how the signal-to-noise (SNR) scaleable coder can benefit from optimizing quantified discrete cosine transform (DCT) coefficients, in a rate-distortion context, in order to reduce bit-rate overheads. The technique is based on adjusting the quantized coefficients rather than dropping them, since the former gives finer control over rate-distortion trade-offs. The widely used Lagrangian optimization technique is then applied to arrive at the optimally adjusted coefficients block. We show that such an optimization is very efficient for the second layer, but has little effect on the base layer.
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A coding method for wavelet coefficients of images using vector quantization, called successive approximation vector quantization (SA-W-VQ) is proposed. In this method, each vector is coded by a series of vectors of decreasing magnitudes until a certain distortion level is reached. The successive approximation using vectors is analyzed, and conditions for convergence are derived. It is shown that lattice codebooks are an efficient tool for meeting these conditions without the need for very large codebooks. Regular lattices offer the extra advantage of fast encoding algorithms. In SA-W-VQ, distortion equalization of the wavelet coefficients can be achieved together with high compression ratio and precise bit-rate control. The performance of SA-W-VQ for still image coding is compared against some of the most successful image coding systems reported in the literature. The comparison shows that SA-W-VQ performs remarkably well at several bit rates and in various test images.
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The behavior of linear phase wavelet transforms in low bit-rate image coding is investigated. The influence of certain characteristics of these transforms such as regularity, number of vanishing moments, filter length, coding gain, frequency selectivity, and the shape of the wavelets on the coding performance is analyzed. The wavelet transforms performance is assessed based on a first-order Markov source and on the image quality, using subjective tests. More than 20 wavelet transforms of a test image were coded with a product code lattice quantizer with the image quality rated by different viewers. The results show that, as long as the wavelet transforms perform reasonably well, features like regularity and number of vanishing moments do not have any important impact on final image quality. The influence of the coding gain by itself is also small. On the other hand, the shape of the synthesis wavelet, which determines the visibility of coding errors on reconstructed images, is very important. Analysis of the data obtained strongly suggests that the design of good wavelet transforms for low bit-rate image coding should take into account chiefly the shape of the synthesis wavelet and, to a lesser extent, the coding.
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A block-based subband image coder that exploits the ability to perform decimation in the discrete cosine transform (DCT) domain to effect a pyramidal data structure is described. The proposed "DCT pyramid" has a distinct feature of improved image rendition properties without the associated blocking artifacts at low bit-rates.
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Measurements of subjective picture impairment as a function of network loading in a simulated ATM network are reported. The simulation indicated that cells tend to be discarded in bursts, the frequency and severity of which can be related to the loading by a threshold model. The effect of the discards on broadcast-style video, coded using a single-layer H.261-type method, was found to be a function of scene content and movement at the instant of occurrence. If the visibility of cell discards is maintained at or below threshold in worst-case scenes, the study indicated that network loadings around 55% for a multiplex of 16 video sources and around 70% for a multiplex of 48 video sources are achievable.