High Frequency Area Research Articles

Rapidly pulsed reductants for diesel NOx reduction with lean NOx traps: Effects of pulsing parameters on performance

The use of Rapidly Pulsed Reductants (RPR) provides a method for injecting hydrocarbons in rapid pulses ahead of a lean NOx trap (LNT) with the goal of achieving greater than 90% NOx conversion at temperatures as high as 600°C. This approach was recently discussed under the name Di-Air by Toyota. It may be useful for diesel vehicles with smaller engines that cannot conveniently accommodate urea SCR technology. A further goal of RPR is to reduce the fuel penalty associated with the fuel injections used to purge the LNT.The focus of this study was on understanding this approach in the exhaust temperature range of 450°C to 600°C. The impact of pulsing parameters, i.e., pulse frequency, pulse amplitude, and duty cycle (i.e., ratio of pulse-on/total-cycle-time) on RPR performance was investigated using ethylene injection into simulated exhaust with a research LNT catalyst over a wide range of conditions. A novel injection system was designed that allowed for the investigation of previously unexplored areas of high frequency (up to f=100Hz) and produced pulse durations as short as a millisecond. NOx storage capability was found to be essential for RPR operation. An optimal pulsing frequency was always found for a given set of flow conditions that produced a maximum NOx conversion while holding the fuel penalty (i.e., hydrocarbon dose) constant. The optimal pulsing frequency, usually on the order of 1Hz, was dependent on a number of parameters including the flow velocity, concentration of injected hydrocarbons, and operating temperature. The effects of pulse duty cycle and amplitude, which together determine the amount of injected reductant or the fuel penalty, were investigated separately. Regardless of pulsing frequency and duty cycle, pulses of injected hydrocarbon large enough in magnitude to generate a rich mixture were necessary during the pulse in order to achieve high NOx conversion. Lean or even stoichiometric pulses did not achieve significant NOx conversion. However, even with the rich pulses, the cycle-averaged air/fuel ratio remained net lean in this work.In the main temperature range of this study (450–600°C), where the NOx storage capacity of the LNT was very limited, RPR operation could be divided into two frequency regimes, one below and one above the optimum frequency. At injection frequencies below the optimum frequency, it was observed that the NOx conversion improved as the frequency increased. This was primarily because the duration of the lean period was decreasing, increasing the average NOx storage efficiency during the lean period while still maintaining sufficient durations of the rich period to adequately purge the LNT. At injection frequencies above the optimum frequency, reductant mixing and its parasitic consumption by the gas phase O2 resulted in inadequate purging of the LNT, causing the NOx conversion to drop from the maximum value. These competing factors led to the maximum NOx conversion observed during RPR operation for a LNT at temperatures as high as 600°C for a specified fuel penalty.

Quantitative estimation of resource nationalism by binary choice logit model for panel data

Since the beginning of this century, another new wave of resource nationalism with unprecedented high frequency and wide area had been profoundly affecting natural resources industry's room of development. It attracted increased attention among researchers and business investors. Numerous descriptive case studies on the issue indicated us how specific economic, political and other factors interacted and further drove resource nationalism strategy and policy making. However, as far as we know, none of them were able to quantitatively dig out the mutual factors across countries that work uniformly in producing resource nationalism. The objective of the study is quantifying significant factors dominating the occurrence of resource nationalism for important metal and energy resources producing countries at global level by binary choice logit model for panel data. Besides finding out the significant variables and their marginal effects to resource nationalism from 2000 to 2013, the regression helps predict up to 89 resource producing countries’, 5 types of base metals’, 4 types of precious metals’, and 3 types of energy resources’ probability of resource nationalism during 2003–2012. The study is a primary trial of researching on resource nationalism and provides some insights for theoretical building and genetic simulation on the issue.

Propagation of meandering rotors surrounded by areas of high dominant frequency in persistent atrial fibrillation

Identification of arrhythmogenic regions remains a challenge in persistent atrial fibrillation (persAF). Frequency and phase analysis allows identification of potential ablation targets. This study aimed to investigate the spatiotemporal association between dominant frequency (DF) and reentrant phase activation areas. A total of 8 persAF patients undergoing first-time catheter ablation procedure were enrolled. A noncontact array catheter was deployed into the left atrium (LA) and 2048 atrial fibrillation electrograms (AEGs) were acquired for 15 seconds following ventricular far-field cancellation. DF and phase singularity (PS) points were identified from the AEGs and tracked over consecutive frames. The spatiotemporal correlation of high DF areas and PS points was investigated, and the organization index at the core of high-DF areas was compared with that of their periphery. The phase maps presented multiple simultaneous PS points that drift over the LA, with preferential locations. Regions displaying higher PS concentration showed a degree of colocalization with DF sites, with PS and DF regions being neighbors in 61.8% and with PS and DF regions overlapping in 36.8% of the time windows. Sites with highest DF showed a greater degree of organization at their core compared with their periphery. After ablation, the PS incidence reduced over the entire LA (36.2% ± 23.2%, P < .05), but especially at the pulmonary veins (78.6% ± 22.2%, P< .05). Multiple PS points drifting over the LA were identified with their clusters correlating spatially with the DF regions. After pulmonary vein isolation, the PS's complexity was reduced, which supports the notion that PS sites represent areas of relevance to the atrial substrate.

Frequency characteristics of the semicicular canals damage in patients with Meniere disease

Objective: To evaluate semicircular canal damage and its frequency characteristics in Meniere disease patients. Methods: Sixty-seven Meniere disease patients accepted the video-head impulse test(vHIT)which responses to semicircular canal function of high frequency area, head shaking test(HST) which responses to semicircular canal function of middle frequency area, and caloric test(CT) which responses to semicircular canal function of low frequency area.Preferences were recorded including the video head impulse test gain (vHIT-G), head shaking nystagmus (HSN) and parameters of the unilateral weakness (UW) as observation index, and results of all the three tests were analyzed according to Meniere disease patients. SPSS 17.0 software was used to analyzed the data. Results: The positive rate of CT, HSN and vHIT were 70.1%(47/67), 41.8%(28/67) and 23.9%(16/67) respectively. Comparation of the positive rate among CT, HST and vHIT showed statistically significant difference (χ2=10.93, P=0.001; χ2=28.79, P=0.000). Comparation of the positive rate between HST and vHIT showed statistically significant difference(χ2=4.87, P=0.027). Conclusions: Semicircular canal function damage in Meniere disease patients mainly presents in the low frequency area, which indicates a characteristic phenomenon that low-frequency function area (caloric test results) is more predisposed to be involved than that of middle-frequency function area (head shaking testing)and high-frequency function area (video head impulse testing) in Meniere disease patients.

Independent tonotopy and thalamocortical projection patterns in two adjacent parts of the classical primary auditory cortex in mice

Amid recent amendment of delineation of a mouse auditory cortical map, a caudal auditory field, originally defined as the primary auditory cortex (AI), was divided into the AI and dorsomedial field (DM), based on distinct high frequency areas. A low frequency area was not previously established in the DM because responses to low frequency tones were weak in this area. This may lead to the misconception that the DM is an atypical region that lacks a low frequency band. In the current study, we confirmed that the DM has a low frequency area that is completely independent from the AI. First, we conducted flavoprotein fluorescence imaging with improved signal to noise ratio and revealed the presence of two separated low frequency areas in the AI and DM. Next, we injected a retrograde neural tracer along the tonotopic axis of the AI or DM to reveal the thalamic origins in the ventral division of the medial geniculate body (MGv). We found that neurons projecting to low frequency areas of the AI and DM occupied different locations within the MGv and mutually independent topographic organizations consisting of thalamic neurons projecting to the AI or DM. These results indicate that the AI and DM have distinct low frequency areas with distinct thalamic projections from the MGv. Our findings reaffirm that the AI and DM should be regarded as independent regions in the mouse auditory cortex.

Thermal weathering of granite spheroidal boulders in a dry‐temperate climate, Northern Dobrogea, Romania

AbstractWeathering microforms associated with exfoliation were investigated on 40 granitic spheroidal boulders identified on Pricopan Ridge (Măcin Mountains) in order to establish a spatial distribution pattern. Continuous thermal monitoring allowed the frequency and intensity distribution assessment of short‐term temperature changes triggered by summer storms, of intense day–night amplitudes and frost cycles across a uniform rounded boulder. Rock strength estimated by Schmidt hammer tests differentiates a significantly weaker resistance on the southern face of the boulders (rebound values of 27 to 33) in comparison with the northern face (43–50). The lowest resistance of the north–south cross‐boulder profile corresponds to the southern gentle slopes (0°–45°) thus defining the most susceptible area to exfoliation and other weathering processes. It is argued that this low‐resistant sector fits well with the maximum frequency and intensity of thermal processes recorded on the low and mid slopes (0°–45°) of the boulders south side, with small differences from one process to another, whilst the sector of 20° to 30° south corresponds to the peak activity of all. In accordance, the overlay map of exfoliated surfaces places the high frequency area on a spherical cap developed similarly (between 5° north and 45° south). The smallest exfoliated surfaces normally appear around 30° south and are inferred to extend in time both to the boulder top and downslope. The correlations between the frequency/intensity maps of thermal processes and the frequency map of exfoliated surfaces point to a complementary action in the exfoliated surfaces development of the short‐term temperature changes and diurnal cooling and heating due to the directional insolation effect, as similarly inferred in the development of meridional cracks. Copyright © 2016 John Wiley &amp; Sons, Ltd.

A study of analysis words meaning, which select"frequent use in modern Korean Research"above high frequency area, by Han - character’s Korean meaning

A study of analysis words meaning, which select"frequent use in modern Korean Research"above high frequency area, by Han - character’s Korean meaning

Creating a Screening Measure of Health Literacy for the Health Information National Trends Survey

Create a screening measure of health literacy for use with the Health Information National Trends Survey (HINTS). Participants completed a paper-based survey. Items from the survey were used to construct a health literacy screening measure. A population-based survey conducted in geographic areas of high and low minority frequency and in Central Appalachia. Two thousand nine hundred four English-speaking participants were included in this study: 66% white, 93% completed high school, mean age = 52.53 years (SD = 16.24). A health literacy screening measure was created using four items included in the HINTS survey. Scores could range from 0 (no questions affirmative/correct) to 4 (all questions answered affirmatively/correctly). Multiple regression analysis was used to determine whether demographic variables known to predict health literacy were indeed associated with the constructed health literacy screening measure. The weighted average health literacy score was 2.63 (SD = 1.00). Those who were nonwhite (p = .0005), were older (p < .0005), or had not completed high school (p < .0001) tended to have lower health literacy screening measure scores. This study highlights the need to assess health literacy in national surveys, but also serves as evidence that screening measures can be created within existing datasets to give researchers the ability to consider the impact of health literacy.

Preparation of NiO Nanosheets by Hydrothermal Method and its Electrochemical Capacitive Properties

The precursor Ni (OH)2 was synthesized by a simple hydrothermal method with NiSO4•6H2O and (CH2)6N4 as reactants. Both concentrations of reactants are 0.02 M, 0.04 M, 0.06 M, 0.08 M for experiment contrast, and then NiO was gained after calcination at 400°C. The phase and morphology of the synthesized product were characterized by X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM). The electrochemical capacitive characterization was performed using cyclic voltammetry (CV), galvanostatic charge/discharge (GCD) and electrical impedance spectroscopy (EIS) measurements in a 6mol/L KOH aqueous solution electrolyte. The result shows that with the increase of concentrations of reactants, nanosheets stack together and turn into thick slices. CV curves have obvious redox peak, the GCD curves are nonlinear and EIS curves of high frequency area are semicircle. From electrochemical analysis, the capacitance type is pseudocapacitance. And a maximal specific capacitance value when two reactants concentration both are 0.08 M which the specific capacitance decreases from 97 F/g (at a current density of 0.3A/g) to 56 F/g (at a current density of 1 A/g).

可用于分布式电源并网的双频逆变器研究

为提高分布式电源并网的效率，减小并网电流总的谐波畸变率，降低并网逆变器的开关损耗，研究了一种新型双频并网逆变器，其中一部分工作在低频，采用电流滞环控制，快速跟踪高频单元电流，传递大部分功率；另一部分工作在高频，采用空间矢量调制，改善并网电流的动态性能，使并网电流和电网电压同频同相，并且实现了电流有功分量和无功分量的解耦控制。以双频逆变器A相工作的四种状态为例分析了系统的工作原理。Simulink仿真模型验证了双频并网逆变器能够大大降低开关损耗，使并网电流总的谐波畸变率减小，提高了并网效率。 A new type topology of dual-frequency photovoltaic grid-connected inverter is researched to improve the efficiency of distributed power grid-connected and reduce the total harmonic distortion rate of the gird-connected current and the switching losses. Part of it works in the low-frequency area to fast-track high-frequency cell current and transit most of the power by using current hysteresis control. The other part works in the high frequency area to improve the dynamic performance of the distributed power grid connected current and make grid-connected current in the same phase and frequency with grid voltage. The voltage and currents changes are analyzed in four work states of phase A. The Simulink model verifies the switching losses and the harmonic distortion rate is greatly reduced; thus grid-connected efficiency is improved.

Experimental research of mechanical behavior of porcine brain tissue under rotational shear stress

The objective of this paper is to investigate mechanical behavior of porcine brain tissue with a series of rotational shear stress control experiments. To this end, several experiments including stress sweep tests, frequency sweep tests and quasi-static creep tests were designed and conducted with a standard rheometer (HAAKE RheoStress6000). The effects of the loading stress rates to mechanical properties of brain tissue were also studied in stress sweep tests. The results of stress sweep tests performed on the same brain showed that brain tissue had an obvious regional inhomogeneity and the mechanical damage occurred at the rotational shear stress of 10–15Pa. The experimental data from three different loading stress rates demonstrated that the mechanical behavior of porcine brain tissue was loading stress rate dependent. With the decrease of loading stress rate, a stiffer mechanical characteristic of brain tissue was observed and the occurrence of mechanical damage can be delayed to a higher stress. From the results of frequency sweep tests we found that brain tissue had almost completely elastic properties at high frequency area. The nonlinear creep response under the rotational shear stress of 1, 3, 5, 7 and 9Pa was shown in results of creep tests. A new nonlinear viscoelastic solid model was proposed for creep tests and matched well with the test data. Considering the regional differences, loading stress rates and test conditions effects, loss tangent tan δ in porcine brain tissue showed a high uniformity of 0.25–0.45.

Chemoprophylaxis of Dirofilaria immitis (Leidy 1856) infection at a high challenge environment.

BackgroundThe frequency of canine heartworm infection in the state of Rio de Janeiro, Brazil was high before chemoprophylactic treatment was available, with one of the highest rates of infection (52.5 %) found among dogs living on the eastern shore of the state. Following the launch of a chemoprophylactic product, the rate of infection gradually decreased, and new infections were rarely reported. After 2005, outbreaks reported at the eastern shore as well as for new infections in other areas of high infection frequency were considered to possibly be related to reduced efficacy of macrocyclic lactones. Therefore, this study aimed to evaluate the efficacy of topical heartworm preventatives from different drug families at the high challenge area of the state of Rio de Janeiro.MethodsA total of 46 dogs, including animals negative for Dirofilaria immitis microfilariae and antigen (Snap 4 Dx, IDEXX Laboratories, USA) at the initial screening were randomly allocated to two monthly treatment groups. Dogs in one group received topical moxidectin + imidacloprid and dogs in the other group received topical selamectin for eight consecutive months. Blood samples were obtained for microfilariae and antigen detection until the eleventh month after the first treatment. Dogs becoming microfilaremic or antigenemic on or before day 180 were considered to be infected prior to the first dose and were excluded from the study.ResultsA total of 29 dogs completed the study, including 14 treated with moxidectin + imidacloprid and 15 treated with selamectin. No dogs treated with moxidectin + imidacloprid (0/14) became infected during the treatment period, whereas four dogs of the selamectin group (4/15) became infected.ConclusionTopical moxidectin + imidacloprid is 100 % effective in preventing D. immitis infections in dogs living in a high challenge natural environment.

Dielectric properties of nanocomposite (Cu)x(SiO2)(100−x) produced by ion-beam sputtering

It has been established that in the nanocomposite Cux(SiO2)(100−x) with the metallic phase content x = 27.27 at.% the following phenomena occur: hopping conductivity, additional polarity and coilless-like inductance. Coilless-like inductance phenomenon consists in the occurrence of positive values of phase shift in the high frequency area. Activation energy of the dielectric relaxation time for copper nanoparticles of unoxidized surface is of approx. 0.0003 eV, whereas surface oxidation causes a potential barrier occurrence and activation energy increase up to approx. 0.3360 eV. Comparative analysis of results obtained for the Cux(SiO2)(100−x) material and the measurements results obtained for the nanocomposites (FeCoZr)x(Al2O3)(100−x), (FeCoZr)x(CaF2)(100−x) and (FeCoZr)x(PZT)(100−x), which containing nanoparticles of ferromagnetic alloy, has been performed. It has shown that the type of magnetic properties of metallic phase, which is ferromagnetic ones for FeCoZr and diamagnetic ones for Cu, does not affect capacitive and inductive phenomena of the nanocomposites. The phenomena are related only to the nanogranular structure of the materials and the hopping mechanism of the charge transport between the metallic phase nanoparticles.

Impact analysis of LTCC materials on microstrip filters’ behaviour up to 13 GHz

Purpose – The purpose of this paper is to consider the adequacy of various microstrip filters’ behaviour based on different low-temperature co-fired ceramic (LTCC) dielectrics in the high frequency (HF) area up to 13 GHz. Design/methodology/approach – Low pass, band pass and band stop filters for ultra-wideband radar systems were designed, simulated, fabricated and measured using three various dielectric substrates: Dupont GreenTape 951, Dupont GreenTape 9K7 and Murata LFC. Findings – It is not possible to unambiguously determine the most suitable LTCC dielectric for these filter design because, in general, all designed filters fulfilled requirements (attenuation, cut off frequencies) with minimal divergences, but temperature-stable dielectric and physical properties of Murata LFC make them a promising ceramic for HF application (repeatability of realised experiments). Originality/value – The novelty of this work lies in unconventional usage of LTCC as material with defined dielectric properties proper for HF applications.

Impedance model of metal-dielectric nanocomposites produced by ion-beam sputtering in vacuum conditions and its experimental verification for thin films of (FeCoZr)x(PZT)(100−x)

The paper presents results of testing electric properties (resistance, capacity and phase angle in an equivalent parallel circuit) of ferromagnetic alloy-dielectric nanocomposites (FeCoZr)x(PZT)(100−x) produced by ion-beam sputtering in vacuum conditions. The measurements have been performed using alternating current within the frequency range of 50 Hz–1 MHz for measuring temperatures ranging from 77 K to 373 K. In nanocomposites (CoFeZr)x(PZT)(100−x), produced by ion beam sputtering using a beam of combined argon and oxygen ions, for x approaching the percolation threshold, frequency dependences of the phase angle φ that resemble those occurring in RLC parallel circuits have been observed. In the low frequency area, the phase angle of 90° ≤ φ < 0° occurs. It corresponds to the capacitive type of conduction. In the high frequency area, the inductive type of conduction with 0° ≤ φ ≤ 90° occurs. At the resonance frequency f0, characterized by the phase angle of φ = 0°, the capacity value reaches its strong local minimum. A theoretical basis for a model of the AC hopping conduction for metal-dielectric nanocomposites has been developed and on that basis frequency dependences of the phase angle, resistance and capacitive current density components have been analyzed. The obtained theoretical and experimental results have been compared.

Learning ramp transformation for single image super-resolution

We propose the use of explicitly identified image structure to guide the solution of the single image super-resolution (SR) problem. We treat the image as a layout of homogeneous regions, surrounded by ramp edges of a larger contrast. Ramps are characterized by the property that any path through any ramp pixel, monotonically leading from one to the other side, has monotonically increasing (or decreasing) intensity values along it. Such a ramp profile thus captures the large contrast between the two homogeneous regions. In this paper, the SR problem is viewed primarily as one of super-resolving these ramps, since the relatively homogeneous interiors can be handled using simpler methods. Our approach involves learning how these ramps transform across resolutions, and applying the learnt transformations to the ramps of a test image. To obtain our final SR reconstruction, we use the transformed ramps as priors in a regularization framework, where the traditional backprojection constraint is used as the data term. As compared to conventional edge based SR methods, our approach provides three distinct advantages: (1) Conventional edge based SR methods are based on gradients, which use 2D filters with heuristically chosen parameters and these choices result in different gradient values. This sensitivity adversely affects learning gradient domain correspondences across different resolutions. We show that ramp profiles are more adaptive, stable and therefore reliable representations for learning edge transformations across resolutions. (2) Existing gradient based SR methods are often unable to sufficiently constrain the absolute brightness levels in the image. Our approach on the other hand, operates directly in the image intensity domain, enforcing sharpness as well as brightness consistency. (3) Unlike previous gradient based methods, we also explicitly incorporate dependency between closely spaced edges while learning ramp correspondences. This allows for better recovery of contrast across thin structures such as in high spatial frequency areas. We obtain results that are sharper and more faithful to the true image color, and show almost no ringing artifacts.

Magnetic Circuit of a High-Voltage Transformer up to 10 kHz

Power and energy measurements in smart grids require a measurement system capable of performing signal processing at the higher harmonic frequencies that are present in power grids. For the calibration process of instrument voltage transformers, or high-voltage dividers, it is necessary to have a high-voltage source with an appropriate frequency range. The fundamental element of such a source is the output high-voltage transformer operating at a nominal voltage of 10 kV and in the frequency range from 200 Hz up to 10 kHz. The output current is assumed to be lower than 20 mA. This paper focuses on the design and realization of the magnetic circuit of the transformer described above. Trafoperm, ferrite or nanocrystalline materials can be used for the frequency range considered here. Ferrite materials usually reach saturation at a magnetic flux density of 0.2 T with very low permeability values, while trafoperm material usually suffers from unacceptable power losses in higher frequency areas. This is the main reason why these materials are not suitable for use in a wide range of frequencies, and some combined magnetic cores must be used. The proposed solution is based on magnetic cut C type cores made from nanocrystalline alloy (VITROPERM 500), which behaves better in the frequency range under consideration. The magnetic parameters of this material were measured and compared with trafoperm, and then, the 10 kV high-voltage transformer was designed and manufactured.

A bundled-optimization model of multiview dense depth map synthesis for dynamic scene reconstruction

Depth map is the basic requirement for all three-dimensional (3D) applications, but facing sensor noises, low frame-rate and low resolution in the procedure of data acquisition, especially in multiview cases. These problems bring obstacles to high quality 3D applications. Among the existing approaches, depth propagation is one of the promise approaches, and it can be utilized in temporal or spatial manner. However, propagation based algorithms process one aspect of the mentioned problems to pursuit local optimal solution. Actually, the process chain of depth map is from capture to application, and the optimization should be coupled instead of mutually independent. In this paper, we proposed a bundled-optimization scheme to process the thorough chain from capture to multiview dense depth map generation for the 3D applications. In this scheme, sensor noises in the captured low-resolution depth map are first detected and removed through a frequency-counting based non-linear filter. The filter refrains from the noise amplification in the procedure of depth map up-sampling. Low-pass blurring effect around high frequency areas is the by-product in up-sampling, and it is hard to detect in the depth map. We therefore propose a Blocklet based depth map optimization method for this blurring effect, and the accuracy of the high resolution depth map is then improved. Temporal depth propagation is then utilized on the optimized depth maps through the optical flow field rectified by temporal and spatial constrains. After that, a multi-set graph cut model is proposed to synthesize the multiview dense depth map. The experimental results indicate that our scheme can achieve at least 13.2575% PSNR gains when comparing to the benchmark depth map synthesis methods, and suggest the effectiveness of the proposed bundled-optimization method.

73 * Ablation for persistent atrial fibrillation shrinks left atrial high dominant frequency areas

Introduction: The dominant frequency (DF) of atrial electrograms (EGMs) is believed to reflect atrial substrate with periodic activation responsible for the maintenance of persistent atrial fibrillation (persAF). This study assessed whether ablation for persAF affected DF spatio-temporal behaviour using global simultaneous non-contact mapping. Methods: Five patients with symptomatic longstanding persAF (duration of 34±25 months) undergoing first time ablation were recruited. A non-contact array catheter (EnSite Array, St. Jude Medical) was deployed in the left atrium (LA) both pre- and post-pulmonary vein isolation, but prior to any other substrate modification. Virtual unipolar EGMs were collected simultaneously from 2048 nodes on the LA geometry.After ventricular far-field influence cancellation, fast Fourier transform was used to determine the DF for each EGM. DF was defined within the range of 4Hz to 10 Hz (4 s time window; 50% overlap; up to 38 s per patient). Highest DF (HDF) regions for each individual window were defined as any LA geometry nodes where the calculated DF was within 0.25 Hz of the maximum DF measured for that window. The spatio-temporal behaviour of the HDF areas was studied pre- and post-ablation by assessing the proportion of time for which each node was defined as a HDF region, and compared using the paired-samples t-test. Results: Prior to ablation, considering all patients, an average of 24.5% of the LA was defined as an HDF area for any given time. This decreased significantly to 11.2% post-ablation (p<0.001). Figure 1 represents the spatio-temporal distribution of HDF clouds on the 3D LA geometry seen in one patient, before and after ablation. The colorbar represents the percentage of the total time for which HDF is hosted at that node. Figure 2 shows the change in the average proportion of the LA hosting HDF for each patient (pre- and post- ablation) per time window. Conclusion: PersAF ablation significantly reduces HDF spatio-temporal coverage in the LA. This extends the findings of previous point-by-point ablation studies, and may support a DF-targeted ablation strategy using global simultaneous mapping for persAF. ![Graphic][1] Figure 1. ![Graphic][2] Figure 2 Proportion of the LA hosting HDF (%) [1]: /embed/inline-graphic-1.gif [2]: /embed/inline-graphic-2.gif

Frequência espaço-temporal dos focos ativos em Minas Gerais durante o período de 1999 a 2009

Neste estudo, objetivou-se resgatar o histórico de focos ativos no estado de Minas Gerais, durante os anos de 1999 e 2009 para uma análise exploratória dos dados. Por meio de análise temporal, procedeu-se a uma análise dos meses e anos em que os focos foram mais frequentes, e do período crítico de ocorrência de focos ativos. Já, a análise espacial considerou a frequência e a densidade de focos ativos nos Núcleos do Instituto Estadual de Florestas (IEF). No caso das Unidades de conservação, analisou-se também a recorrência anual. No total, foram detectados 67.334 focos ativos em MG, no período de 1999 a 2009. A análise temporal revelou que o ano de 2003 apresentou o maior frequência, totalizando 10.929 focos, enquanto o ano de 2009 apresentou apenas 2.378 focos. O mês de maior frequência foi outubro com 24.149 focos registrados. As áreas com maior frequência, maior densidade e maior recorrência de focos ativos (neste último caso só em unidades de conservação), são consideradas mais críticas quanto aos focos ativos. Porém, a baixa frequência de focos e a alta densidade também são apontamentos de áreas críticas. Nas áreas de maior frequência de focos e baixa densidade, o tamanho da área influenciou diretamente na elevada ocorrência de focos ativos. Nessas áreas, sugere-se uma análise de distribuição espacial para verificar se os focos ativos estão concentrados ou esparsos. O melhor cenário aqui apresentado é baixa frequência e densidade de focos ativos.