Evaluation of the B‐method for determining actual evapotranspiration in a boreal forest from MODIS data

Boreal forests occupy about 11% of the terrestrial surface and represent an important contribution to global energy balance. The ground measurement of daily evapotranspiration (LE_d) is very difficult due to the limitations on experiments. The objective of this paper is to present and explore the applicability of the B‐method for monitoring actual LE_d in these ecosystems. The method shown in this paper allows us to determine the surface fluxes over boreal forests on a daily basis from instantaneous information registered in a conventional meteorological tower, as well as the canopy temperature (T _c) retrieved by satellite. Images collected by the MODIS (moderate resolution imaging spectroradiometer) on board EOS‐Terra have been used for this study. The parameters of the model were calibrated from the SIFLEX‐2002 (Solar Induced Fluorescence Experiment 2002) campaign dataset in a northern boreal forest in Finland. A study of these parameters was made on an hourly basis in order to make the method applicable, not only at midday but within an interval of 7 h around it. This is an important advance with respect to the original formulation of this approach since the overpass time of satellites can be very variable. The comparison between T _c ground measured with a thermal infrared radiometer, and T _c retrieved from land surface temperature (LST) MODIS data, showed an estimation error of ±1.4°C for viewing angles from 5 to 60°. A complete sensitivity analysis was carried out and an estimation error of about ±35%, corresponding to the interval 10.00–11.00 h UTC, was shown as the lowest in LE_d retrieval. Finally, the method was validated over the study site using 21 MODIS images for 2002 and 2003. The results were compared with eddy‐correlation ground measurements. An accuracy of ±1.0 mm/day and an overestimation of 0.3 mm/day were shown in the LE_d retrieval.     

High inter‐port isolation dual circularly polarized slot antenna with interdigital capacitor

A planar dual circularly polarized slot antenna is presented. The designed antenna has two tilted “8” shaped slots fed by microstrip lines, one each for transmission (T_X) and reception (R_X) operations. The isolation between the two ports (T_X and R_X) is augmented by means of an interdigital capacitor based bandstop filter. The proposed antenna has an impedance bandwidth of 361 MHz centered at 2.293 GHz (2.113‐2.474 GHz) with the isolation between the ports being >17.6 dB which goes up to a value as high as 46 dB within the band of operation. The 3 dB axial ratio (AR) bandwidth is 11.52% centered at 2.1275 GHz (2.005‐2.25 GHz). Because of its high inter‐port isolation within the AR bandwidth, the design is suitable as a full‐duplex antenna for applications in S‐band.     

High isolation,proximity‐fed monostatic patch antennas with integrated self‐interference cancellation‐taps for ISM band full duplex applications

This work presents two dual polarized proximity‐fed monostatic patch antennas with improved interport isolation for 2.4 GHz industrial, scientific and medical band same frequency full duplex wireless applications. The presented antennas achieves the high interport decoupling through intrinsic isolation of the polarization diversity in conjunction with a simple single‐tap and two‐taps self‐interference cancellation (SIC) topologies. The polarization diversity isolation is achieved through two perpendicular microstrip feeds for proximity feeding to excite orthogonal polarization mode for transmit (T_x) and receive (R_x) modes. The prototype for proposed antenna with integrated single‐tap and two‐taps SIC circuit is tested to record its interport isolation, impedance bandwidths and gains for both T_x and R_x ports. The implemented antenna with single‐tap SIC circuit demonstrates 10 dB return‐loss bandwidth of ≥100 MHz for both T_x and R_x ports. The measured isolation exceeds 40 dB over the 40 MHz bandwidth. Moreover, the recorded peak isolation is better than 74 dB for implemented antenna prototype. Furthermore, the 40 MHz bandwidth with 40 dB isolation can be tuned with the help of SIC‐tap as demonstrated through the experimental results. The measured gain levels are around 4.6 dBi for both T_x and R_x port. The same antenna structure with integrated two‐taps SIC topology features better than 55 dB isolation within 10 dB return loss bandwidth of 100 MHz. The peak isolation exceeds 97 dB and isolation levels are better than 60 and 80 dB over 50 and 20 MHz bandwidths, respectively, for presented antenna with two‐taps SIC configuration. The compact antenna offers comparatively wider impedance and isolation bandwidth with improved SIC levels compared to previous designs.     

Dual‐functional QM SIW cavity integrating two‐element MIMO antenna and second‐order bandpass filter

A quarter‐mode (QM) substrate‐integrated‐waveguide (SIW) cavity is designed as a dual‐functional component. By etching three slots, four sub‐cavities are formed and then two of them with the same size are individually fed by a coaxial port. Three resonating frequencies are excited in the single QM SIW cavity. One of them can radiate cavity energy input by these ports into free space, implying a two‐element multiple‐input‐multiple‐output (MIMO) antenna, whereas the other two can transmit energy from one port to the other port, indicating a second‐order bandpass filter. Moreover, antenna isolation and filter bandwidth can be adjusted to a certain degree. A prototype with the overall size of 0.40λ₀ × 0.40λ₀ × 0.02λ₀ has been fabricated. The integrated bandpass filter demonstrates the measured center frequency of 3.8 GHz and operating bandwidth of 32 MHz while the integrated MIMO antenna exhibits the frequency of 3.4 GHz, bandwidth of 67 MHz, port isolation of 18.0 dB, radiation gain of 4.0 dBi, and envelope correlation coefficient of 0.25.     

Biased scan of plasma display panel for data voltage reduction

This paper proposes a method of reducing the data voltage V_d of plasma display panels (PDPs). The proposed biased-scan method uses two separate ground systems: one for the sustain pulse generator (FGND) and the other for the data address and control systems (CHGND). A dc voltage bias, which is applied between CHGND and FGND during the address period, reduces V_d while preventing the undesired glow discharge induced by a scan pulse only. CHGND is connected to FGND for the first sustain pulse of each subfield, which reduces the time lag of address discharge, but it is separated from FGND for the other sustain pulses to increase the margin of the sustain voltage. The proposed method was tested on a 15% Xe 50-in. Full HD (1920 × 1080) single-scan PDP which had a sustain discharge gap of 110 μm. V_d could be reduced by 20 V (30%), and the power consumption of the V_d voltage source decreased by ∼25 W (50%) from that of the conventional method.     

Radiometric surface temperature calibration effects on satellite based evapotranspiration estimation

Agriculture on the Texas High Plains (THP) uses approximately 89% of groundwater withdrawals from the Ogallala Aquifer, leading to steady decline in water table levels. Therefore, efficient water management is essential for sustaining agricultural production in the THP. Accurate evapotranspiration (ET) maps provide critical information on actual spatio‐temporal crop water use. METRIC (Mapping Evapotranspiration at High Resolution using Internalized Calibration) is a remote sensing based energy balance method that uses radiometric surface temperature (T _s) for mapping ET. However, T _s calibration effects on satellite based ET estimation are less known. Further, METRIC has never been applied for the advective conditions of the semi‐arid THP. In this study, METRIC was applied and predicted ET was compared with measured values from five monolithic weighing lysimeters at the USDA‐ARS Conservation and Production Research Laboratory in Bushland, Texas, USA. Three different levels of calibration were applied on a Landsat 5 Thematic Mapper's thermal image acquired on 23 July 2006 to derive T _s. Application of METRIC on a MODTRAN calibrated image improved the accuracy of distributed ET prediction. In addition, ET estimates were further improved when a THP‐specific model was used for estimating leaf area index. Results indicated that METRIC performed well with ET mean bias error±root mean square error of 0.4±0.7 mm d^?1.     

On the instability in the dimension of splines spaces over T-meshes

The present paper reveals the instability in the dimension of the spline space S(d₁,d₂,d₁−1,d₂−1,T) over certain types of T-meshes T, that is, the dimension is related to not only the topological information of T but also the geometry of T. This insight suggests us to pay much attention to the structure of the T-meshes in modeling with splines over T-meshes.     

Use of self‐erase discharges for high‐speed and low‐voltage addressing of PDPs

Abstract— A technique called “self‐erase‐discharge addressing” has been incorporated with a address‐while‐display driving scheme, contiguous subfield, and erase addressing to obtain high‐speed and low‐voltage addressing of PDPs. The technique uses a relatively high X‐sustain pulse voltage VXsus, which produces a weak self‐erase discharge at its trailing edge. An application of a data pulse Vdata synchronous to a weak self‐erase discharge results in full erase discharge and eliminates all the wall charges. The technique assures a wider operating‐voltage margin since it provides identical amounts of priming charges as well as wall charges to all the horizontal scan lines just prior to addressing. The priming charges are generated by the weak self‐erase discharges, resulting in low Vdata of 30 V and a high addressing speed of 0.66 μsec for a Ne + 10% Xe PDP. V_Xsus = 245 V, and the voltage margins of Vdata and VXsus were 35 and 16 V, respectively. For a 30% Xe PDP, Vdata and VXsus were 30 and 335 V, respectively, with an addressing speed of 1.0 μsec. In order to obtain high dark‐room contrast, it is essential to use ramp reset pulses, with which erase addressing cannot be achieved. By adopting the write addressing only to the first subfield and the self‐erase‐discharge addressing to the subsequent subfields, a peak and background luminance in green of 3100 and 0.22 cd/m², respectively, were obtained with a dark‐room contrast of 14,000:1. The number of subfields was 28, and the light emission duty was 83%. The number of ramp reset pulse drivers could be reduced to 12 by adopting the common reset pulse technique.     

Linearly tapered meander line cross dipole circularly polarized antenna for UHF RFID tag applications

In this article, a circularly polarized antenna for ultra‐high frequency radio frequency identification (RFID) tag is presented. The circular polarization is realized by two orthogonal, unequal length linearly tapered meander line cross dipoles. The meander structure with capacitive tip loading is used for size miniaturization of the antenna. A modified T‐match network is employed to feed the cross dipole structure. The measured 10‐dB return loss bandwidth of the cross dipole antenna is 17 MHz (908‐923 MHz) and the corresponding 3‐dB axial ratio bandwidth is 6 MHz (912‐918 MHz). The overall size of the proposed antenna is 0.17λ₀ × 0.17λ₀ at 915 MHz. The maximum read range between the reader and the tag with the proposed antenna is 4.7 m larger than the analogous linearly polarized tag antenna due to the reduction in polarization loss between the tag and reader antennas. Thus, a maximum read range of 15.66 m with the gain of 1.28 dBic is achieved at 915 MHz.     

A Simple Optimal Parallel Algorithm for a Core of a Tree

A core of a tree T = (V, E) is a path in T which minimizes ∑_vVd(v, P), where d(v, P), the distance from a vertex v to path P, is defined as min_uPd(v, u). We present an optimal parallel algorithm to find a core of T in O(log n) time using O(n/log n) processors on an EREW PRAM machine, where n is the number of vertices of tree T.     

A low volume flexible CPW‐fed elliptical‐ring with split‐triangular patch dual‐band antenna

In this article, the intensive investigations are carried out on a low volume compact flexible antenna for wireless applications with a novel structure model. The proposed model has considered as an elliptical‐ring with split‐triangular patch (ERSTP) antenna with the coplanar waveguide feeding to achieve dual‐bands. The ERSTP antenna is designed with polyimide material having the volume (L _a × W _a × h) 99 mm³. The ERSTP antenna resonates with 2.60 GHz and 3.48 GHz frequencies with a reflection coefficient of ?21.92 dB and ?32.14 dB and a gain of 2.39 dBi and 1.75, dBi respectively. The impedance bandwidths are 100 MHz and 330 MHz observed at two frequency bands. The proposed ERSTP antenna has operated on mobile‐worldwide interoperability for microwave access (M‐WiMAX) and worldwide interoperability for microwave access (WiMAX) bands respectively. The simulated and measured results of ERSTP antenna are in good agreement.     

Thermohydraulics of square-section microchannels following a serpentine path

Fully developed laminar flow and heat transfer behaviour in serpentine channels with a square cross-section has been studied using computational fluid dynamics. Studies were performed up to Re=200, beyond which the flow became unsteady. The effect of geometric configuration was examined in detail for Re=110, 0.525<R _c/d<2 and 3.6<L/d<12 (where d is the side length of the square section, R _c is radius of curvature of the serpentine bends, and L is the half-wavelength of the serpentine path). Simulations were carried out at (Pr=0.7, 6.13 and 100) constant wall heat flux (H2 boundary condition) and constant wall temperature (T boundary condition). Dean vortices formed at the bends promote fluid mixing transverse to the main flow direction. This leads to significant heat transfer enhancement (up to a factor of 8 at high Pr and Re) with relatively small pressure-drop penalty (factor of 1.8 at high Re). Increasing R _c/d mitigates these effects while the effect of increasing L/d decreases the frictional penalty without greatly affecting the heat transfer enhancement.     

Aerodynamic drag in field cycling with special reference to the Obree's position

In cycling at race speeds, 90% of total resistance opposing motion, R _T(N) T depends on aerodynamic drag of air, which is directly proportional to the effective frontal area, AC _d(m²). R _T was measured on a cyclist, in an open velodrome, in order to evaluate AC _d in four different positions on a traditional bicycle: upright d position (UP), dropped position (DP), aero position (AP) and Obree's position (OP : the hands in support under the chest, the forearms tucked on the arms, the trunk tilted forward). R _T was determined at different constant speeds, Vc(m s^?1) with a special device (Max One), which allows the measurement of the external mechanical power P _ext(W) in real conditions of cycling locomotion ext (R _T = P _ext Vc^?1). Experiments were carried out in order to test the validity and the reproducibility of P _ext provided by the measurement device. P _ext was measured twice in the same experimental conditions (exercise on a treadmill against slopes varying from 1 to 14%) and no significant difference was observed between the two measurement series. A systematic measurement error was observed allowing the use of a correcting factor. As expected, in the four rider positions, R _T increased linearly (p<0.001, r = 0.90-0.95) with Vc². AC _d were significantly different (p<0.001) between the four positions, except between DP and AP. As compared to UP, in DP, AP and OP the significant reductions of AC _d were 7.8, 12.4 and 27.8%, respectively. These reductions were associated with the degree of rachis flexion and with the decrease of the lateral distance between the two upper limbs. In UP, AC _d (0.299 m²) was lower (-23%) than those reported in previous studies. In DP and AP, AC _d (0.276 m² and 0.262 m², respectively) were similar to those reported in previous studies. In OP, no study allowed a real comparison with the value of AC _d (0.216 m²) found in this study. The average rolling resistance (Rr = 1.95±0.81 N) determined according to the four positions was in line with previous reports. These findings suggest that the position adopted by Obree significantly reduces the aerodynamic drag and, thus, is an important factor in cycling performance.     

Evolutionary Trees and Ordinal Assertions

Sequence data for a group of species is often summarized by a distance matrix M where M[s,t] is the dissimilarity between the sequences of species s and t . An ordinal assertion is a statement of the form ``species a and b are as similar as species c and d ' and is supported by distance matrix M if M[a,b] ≤ M[c,d] . Recent preliminary research suggests that ordinal assertions can be used to reconstruct the evolutionary history of a group of species effectively. However, further research on the mathematical and algorithmic properties of ordinal assertions is needed to facilitate the development and assessment of inference methods that utilize ordinal assertions for reconstructing evolutionary histories. A (weighted ) ordinal representation of a distance matrix M is a (weighted) phylogeny T such that, for all species a , b , c , and d labeling T , d _T (a,b) ≤ d _T (c,d) if and only if M[a,b] ≤ M[c,d], where d _T is the weighted path length when T is weighted, otherwise d _T is the unweighted path length. Hence, an ordinal representation of M is a phylogeny that supports the same ordinal assertions supported by M , and so is the focus of our examination of the mathematical and algorithmic properties of ordinal assertions. As it turns out, ordinal representations are rich in structure. In this paper several results on weighted and unweighted ordinal representations are presented: — The unweighted ordinal representation of a distance matrix is unique. This generalizes the well-known result that no two phylogenies share the same distance matrix [10], [21]. — The unweighted ordinal representation of a distance matrix can be found in O(n ² log ² (n)) time. The algorithm presented improves upon an O(n ³ ) algorithm by Kannan and Warnow [13] that finds binary unweighted ordinal representations of distance matrices. — Under certain conditions, weighted ordinal representations can be found in polynomial time. Received May 11, 1997; revised March 13, 1998.     

Integrated circular polarized microstrip antenna with dual‐mode‐polarization insensitive characteristics

A dual‐mode circularly polarized compact antenna with integrated left‐hand and right‐hand circular polarization (LHCP and RHCP) is presented in this work. A multilayer arrangement of a square patch and square ring structure with an irregular transmission line is analyzed for dual‐band, dual‐CP operation. To realize dual mode propagation the proposed structure is excited using electromagnetic coupling technique. Succeeding proximity feeding with T‐stub match is analyzed, which conveys impedance bandwidth of 180 and 300 MHz within |S₁₁| < ?10 dB at 3.5 and 5.5 GHz. The designed CP elements is suitably arranged with feed line for generating two orthogonal polarization of equal amplitude and a 90° phase difference at both the resonant modes (TM₁₀ and TM₀₁). Alterable LHCP and RHCP performance is realized by altering the compensated position and peculiar angle. Having both LHCP and RHCP polarization this design shows polarization insensitive characteristic. Each LHCP and RHCP antenna element accomplished a 3‐dB AR of 70 and 120 MHz with a gain up to 6 dBi. With a low profile of 0.27λ₀ × 0.27λ₀ × 0.04λ₀, the CP antenna is fabricated, and the performance is validated through experimental analysis. With all the viable characteristics, the antenna is proposed for Wi‐MAX/WLAN communication.     

Amorphous‐silicon thin‐film transistors made at 280°C on clear‐plastic substrates by interfacial stress engineering

Abstract— A process temperature of ～300°C produces amorphous‐silicon (a‐Si) thin‐film transistors (TFTs) with the best performance and long‐term stability. Clear organic polymers (plastics) are the most versatile substrate materials for flexible displays. However, clear plastics with a glass‐transition temperature (T_g) in excess of 300°C can have coefficients of thermal expansion (CTE) much larger than that of the silicon nitride (SiN^x) and a‐Si in TFTs deposited by plasma‐enhanced chemical vapor deposition (PECVD). The difference in the CTE that may lead to cracking of the device films can limit the process temperature to well below that of the T_g of the plastic. A model of the mechanical interaction of the TFT stack and the plastic substrate, which provides design guidelines for avoid cracking during TFT fabrication, is presented. The fracture point is determined by a critical interfacial stress. The model was used to successfully fabricate a‐Si TFTs on novel clear‐plastic substrates with a maximum process temperature of up to 280°C. The TFTs made at high temperatures have higher mobility, lower leakage current, and higher stability than TFTs made on conventional low‐T_g clear‐plastic substrates.     

On stability analysis of systems featuring a multiplicative combination of nonlinear and linear time‐invariant feedback

We show that sufficient conditions for the finite‐gain stability of certain systems featuring a multiplicative combination of memoryless nonlinear feedback and linear time‐invariant feedback, as encountered in some systems' biology prototype applications, can be obtained by building on the Rantzer multipliers. These results are obtained by observing that for all finite energy signals x, the time‐truncated inner product 〈x, H(x)N(x)〉_T is positive for all T>0 if N belongs to a subclass of positive memoryless monotone nonlinearities and if, in addition, H is a Rantzer multiplier. Copyright © 2011 John Wiley & Sons, Ltd.     

Charge‐recombination processes in oligomer‐ and polymer‐based light‐emitting diodes: A molecular picture

Abstract— An overview of our recent work on the mechanisms of singlet and triplet exciton formation in electroluminescent π‐conjugated materials will be presented. According to simple spin statistics, only one‐fourth of the excitons are formed as singlets. However, deviations from that statistics can occur if the initially formed triplet charge‐transfer (CT) excited states are amenable to intersystem crossing or dissociation. Although the electronic couplings between the CT states and the neutral exciton states are expected to be largest for the lowest singlet and triplet excitons (S¹ and T¹, respectively), the possibility for direct recombination into T¹ is always very small due to the large exchange energy. In small molecules, spin statistics is expected to be observed because both singlet and triplet exciton formations proceed via higher‐lying S_n/T_n states with similar electronic couplings and fast formation rates. In extended conjugated chains, however, that the ¹CT → S¹ pathway is faster while the ³CT → ^Tn channels become much slower, opening the route to intersystem crossing or dissociation among the ³CT states.     

Application of ultra wideband RF energy harvesting by using multisection Wilkinson power combiner

In this study, an ultra‐wide band (UWB) energy harvesting circuit was proposed using the Greinacher rectifier circuit. The circuit was designed with Wilkinson power combiner (WPC) for use at two different radio frequency signal inputs. To enable broadband operation, the multisection Chebyshev impedance matching technique was applied in the branches of the WPC circuit. The center frequency was selected 2.2 GHz in the design. In terms of the parameters of reflection, transmission and isolation, the WPC circuit operates in the 0.4 GHz‐3.4 GHz range and the percentage bandwidth has been calculated as 136%. In the designed Greinacher rectifier circuit, power conversion efficiency (PCE) was analyzed for different input powers. When load resistor selected as R = 1500 Ω, the PCE for the input power of 9 dBm was about 70%. The proposed circuit, where WPC and Greinacher rectifier circuits was used together for energy harvesting; was operated in the frequency ranges BW₁ = 0.4‐0.81 GHz, BW₂ = 1.54‐1.84 GHz, and BW₃ = 2.2 GHz‐2.89 GHz. As a power combining application, dual power inputs were applied to the WPC circuit with frequencies of 540 MHz‐1800 MHz, 540 MHz‐2450 MHz, 540 MHz‐2700 MHz, 800 MHz‐1800 MHz, 800 MHz‐2450 MHz and 800 MHz‐2700 MHz. Eventually, approximately 70.5% PCE and 1.65 V output voltage were obtained.     

Effect of pulse frequency on the morphology and nanoindentation property of electroplated nickel films

This paper reports the effect of pulse current with different frequencies on the morphology and mechanical properties of nickel (Ni) films deposited by electroplating. The pulse frequency varies from 0 (DC) to 500 Hz while the duty cycle (T _on/T _off) is 1 during electroplating. The average roughness and deposition rate of Ni films decrease with the increasing frequency. The smoothest Ni surface with average roughness of 16.5 nm is achieved at the frequency of 500 Hz while the deposition rate reaches a nearly stable rate of 0.04 μm/min. The surface concentration of ions does not vary with time at a sufficiently high frequency with a long off time for ion to diffuse onto the surface. It will result in much more nuclei formed on the surface of cathode at a limited growth rate to get small grains for smooth morphology. The nanohardness of Ni film initially decreases rapidly from 3.9 to 1.18 GPa at 0 to 10 Hz, respectively, then increases to about 4.87 GPa in the range of 100–200 Hz, and decreases slowly to 4.0 GPa at 500 Hz. The stiffness of Ni films electroplated by pulse current at 100–200 Hz is higher than that by dc electroplating. The compromised Ni film with smooth morphology, good hardness and proper deposition rate is obtained at frequency of 100–200 Hz under the current density of 3 Adm⁻².