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The post green revolution agriculture is based on generous application of fertilizers and high-yielding genotypes that are suited for such high input regimes. Cereals, like maize (Zea mays L.) are capable of utilizing less than 20% of the applied inorganic phosphate (Pi) - a non-renewable fertilizer resource. A greater understanding of the molecular mechanisms underlying the acquisition, transportation and utilization of Pi may lead to strategies to enhance phosphorus use efficiency (PUE) in field crops. In this study, we selected 12 Pi responsive genes in maize and carried out their comparative transcriptional expression in root and leaf tissues of a hydroponically grown Pi stress tolerant maize inbred line HKI-163, under sufficient and deficient Pi conditions. Pi starvation led to significant increase in root length; marked proliferation of root hairs and lesser number of crown roots. Eleven genes were significantly up or down regulated in Pi deficient condition. The putative acid phosphatase, ZmACP5, expression was up regulated by 162.81 and 74.40 fold in root and leaf tissues, respectively. The RNase, ZmRNS1 showed 115 fold up regulation in roots under Pi deprivation. Among the two putative high affinity Pi transporters ZmPht1;4 was found specific to root, whereas ZmPht2 was found to be up regulated in both root and leaf tissues. The genes involved in Pi homeostasis pathway (ZmSIZ1, SPX1 and Pho2) were up regulated in root and leaf. In light of the expression profiling of selected regulatory genes, an updated model of transcriptional regulation under Pi starvation in maize has been proposed.

Maize is an important crop for billions of people as food, feed, and industrial raw material. It is a prime driver of the global agricultural economy as well as the livelihoods of millions of farmers. Genetic interventions, such as breeding, hybridization and transgenesis have led to increased productivity of this crop in the last 100 years. The technique of genome editing is the latest advancement in genetics. Genome editing can be used for targeted deletions, additions, and corrections in the genome, all aimed at genetic enhancement of crops. The Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/CRISPR associated protein 9 (CRISPR/Cas9) system is a recent genome editing technique that is considered simple, precise, robust and the most revolutionary. This review summarizes the current state of the art and predicts future directions in the use of the CRISPR/Cas9 tool in maize crop improvement.

En nuestro pais, la cavidad oral y orofaringe son los sitios mas comunmente afectados por cancer, debido a la alta prevalencia del consumo de tabaco, especialmente, el tabaco de mascar. El objetivo de este estudio fue evaluar prospectivamente los aspectos clinico-patologicos y morfologicos de los pacientes que acuden con estas malignidades. Se estudiaron 153 pacientes con carcinoma de celulas escamosas de la cavidad oral y orofaringe que fueron tratados en el Servicio de Otorrinolaringologia y Cirugia de Cabeza y Cuello entre enero del 2006 y diciembre del 2007 en Maulana Azad Medical College y hospitales asociados en Nueva Delhi. Se evaluaron pacientes de ambos sexos, 127 hombres (83%) y 26 mujeres (17%) con edades entre 22 a 70 anos. Ciento once pacientes (73%) presentaron carcinoma de la cavidad oral y 42 (27%) carcinomas de la orofaringe. El sitio mas comun de presentacion en la cavidad oral fue la mucosa bucal, mientras que la base de la lengua fue el sitio mas comun de la orofaringe. Entre los canceres de la cavidad oral, 51 (46% cada uno) estaban bien diferenciados y moderadamente diferenciados, mientras que 9 (8%) fueron escazamente diferenciado. Sin embargo, entre los canceres de la orofaringe, 27 (64%) fueron moderadamente diferenciados y 15 (36%) fueron pobremente diferenciados. En total, 73 pacientes se presentaron con adenopatias, de los cuales, 44 pacientes fueron en la cavidad oral y 29 en la orofaringe. Se observo una correlacion significativa entre el sitio (es decir, la cavidad oral u orofaringe) y la presentacion de adenopatias. Cincuenta y nueve pacientes (39%) se presentaron con enfermedad en estadio temprano (estadios I y II), mientras que 94 pacientes (61%) se presentaron con enfermedad en estadio tardio (etapas III y IV). Se observo una correlacion significativa entre el sitio (cavidad oral u orofaringe) y la etapa en la presentacion.

Wireless mesh networks (WMNs) are considered as cost effective, easily deployable and capable of extending Internet connectivity. However, one of the major challenges in deploying reliable WMNs is preventing their nodes from malicious attacks, which is of particular concern as attacks can severely degrade network performance. When a DoS attack is targeted over an entire communication path, it is called a path-based DoS attack. We study the performance impact of path-based DoS attacks by considering attack intensity, medium errors, physical diversity, collusion and hop count. We setup a wireless mesh testbed and configure a set of experiments to gather realistic measurements, and assess the effects of different factors. We find that medium errors have significant impact on the performance of WMNs when a path-based DoS attack is carried out, and the impact is exacerbated by the MAC layer retransmissions. We show that due to physical diversity, a far attacker can lead to an increased performance degradation than a close-by attacker. Additionally, we demonstrate that the joint impact of two colluding attackers is not as severe as the joint result of individual attacks. We also discuss a strategy to counter path-based DoS attacks which can potentially alleviate the impact of the attack significantly.

FCC gasoline obtained from an Indian refinery was analyzed for its quality improvement through catalytic processes. The analysis indicated the presence of high amount of sulfur, olefin and iso-paraffins in the feed that are not suitable for processing through the hydro treatment or hydro-isomerization. Detailed studies indicated that majority of iso-paraffinic and olefinic compounds in the feed boil below 60 °C. The entire range of gasoline is fractionated into light fraction (IBP-60 °C) and heavy fraction (60 °C-FBP). Heavy hydrocarbon fraction exhibited more aromatics and sulfur with comparatively low olefins and iso-paraffins. HDS followed by hydro-isomerization of the heavier fraction resulted in the formation of C 6 –C 9 iso-paraffins through the saturation of olefins and aromatics. Overall, the processed FCC gasoline exhibited more iso-paraffins with low olefins, low aromatics and sulfur, without any loss in octane number.

In this study, 770/890 (87%) e rst-degree relatives from 108 families of hospitalized patients with idiopathic dilated cardiomyopathy (IDC) were screened using clinical examination, electrocardiography and echocardiography. Thirty percent of the patients were born to consanguineous parents. Familial dilated cardiomyopathy (FDC) was found in 7 (6.5%) families, which is lower than the earlier published e gures of 20‐25%. Patients with IDC were younger at presentation (p = 0.002) and were more often associated with parental consanguinity (p = 0.04), but the survival rates of familial patients did not differ signie cantly. Conclusion: Despite the high prevalence of consanguinity, there was a low proportion of FDC in the study population. With the prospects of treatment of asymptomatic IDC to slow the progression of the disease, all family members of newly identie ed IDC patients should receive screening and counselling, with appropriate therapy where indicated.

Wireless local area networks (LANs) are vulnerable to malicious attacks due to their shared medium in unlicensed frequency spectrum, thus requiring security features for a variety of applications even at the cost of quality of service (QoS). However, there is very little work on investigating to what extent system performance is affected by security configurations with respect to mobility scenarios, heterogeneous networks, and different applications. In order to exploit the full potential of existing security solutions, we present a detailed experimental study to demonstrate the impacts of security features on performance by integrating cross-layer security protocols in a wireless LAN testbed with IP mobility. We introduce a quality of protection (QoP) model to indicate the benefits of security protocols and then measure the performance cost of security protocols in terms of authentication time, cryptographic overhead and throughput. Our measurements demonstrate that the effects of security protocols on QoS parameters span a wide range; for example, authentication time is between 0.11 and 6.28 s, which can potentially affect packet loss dramatically. We also find that for the same security protocol throughput in nonroaming scenarios can be up to two times higher than that in roaming scenarios. However, some protocols are robust against mobility with little variation in system performance; thus, it is possible to provision steady service by choosing security protocols when users' mobility pattern is unknown. Furthermore, we provide observations on cross-layer security protocols and suggestions to the design of future security protocols for real-time services in wireless LANs.

The successful deployment of wireless local area networks (WLAN) for high speed data transmission and cellular systems for wide coverage and global roaming has emerged to be a complementary platform for wireless data communications. In order to fully exploit potentials in 3G/WLAN integration, authentication of roaming users crossing different networks, must be coupled with mobility management, which is a challenging, yet not resolved issue. The focus of this paper is on state-of-art solutions to Wi-Fi and cellular networks based on IP infrastructure. Moreover, we introduce a new authentication architecture for fast authentication during inter-networking handoff and large-scale heterogeneous networks. We show that the new architecture can reduce authentication latency significantly and be adaptive to user mobility and traffic. Copyright © 2005 John Wiley & Sons, Ltd.

This paper introduces the mobile Internet protocol (mobile IP), describes the various needs that have led to the emergence of mobile IP, and explains its network architecture. In addition, the paper describes quality of service (QoS) requirements for mobile IP and various solutions proposed for it, and then evaluates these solutions, finding advantages and disadvantages in different scenarios along with issues involved with each. © 2003 Lucent Technologies Inc.

Hexa-coordinate neutral adducts (C 6 F 5 ) 3 SbCl 2 ·L( I ) [L=DMSO, DBSO, Ph 3 AsO, Ph 3 PO, DPF, DMF, Py, 3-Pic, TU] and penta-coordinate cationic complexes [(C 6 F 5 ) 3 Sb(Ph 3 AsO) 2 ][ClO 4 ] 2 ( II ) and [(C 6 F 5 ) 3 Sb(bipy)][ClO 4 ] 2 ( III ) have been synthesised. Molecular adducts are monomeric in benzene and non-electrolyte in acetonitrile. IR spectra and conductance measurement suggest the absence of coordination of ClO 4 group to Sb atom in cationic complexes. Spectroscopic data conform to the requirement of octahedral configuration for neural complexes ( I ) and a trigonal bipyramidal structure for complex cations ( II ) and ( III ).

Many innovative floating offshore structures have been proposed for cost effectiveness of oil and gas exploration and production in water depths exceeding one thousand meters in recent years. One such type of platform is the offshore floating Spar platform. The Spar platform is modelled as a rigid body with six degrees-of-freedom, connected to the sea floor by multi-component catenary mooring lines, which are attached to the Spar platform at the fairleads. The response dependent stiffness matrix consists of two parts (a) the hydrostatics provide restoring force in heave, roll and pitch, (b) the mooring lines provide the restoring force which are represented here by nonlinear horizontal springs. A unidirectional regular wave model is used for computing the incident wave kinematics by Airy’s wave theory and force by Morison’s equation. The response analysis is performed in time domain to solve the dynamic behavior of the moored Spar platform as an integrated system using the iterative incremental Newmark’s Beta approach. Numerical studies are conducted for sea state conditions with and without coupling of degrees-of-freedom.

Oil and gas exploration of large reservoirs in deep water has accelerated the need to explore structures suitable for these depths, which operate more economically in deep water. A Spar platform is one such compliant offshore floating structure used for deep water applications for the drilling, production, processing, storage and offloading of ocean deposits. The Spar is modeled as a rigid body with 6 degrees-of-freedom, connected to the sea floor by multi-component catenary mooring lines, which are attached to the Spar at the fairleads. The response-dependent stiffness matrix consists of three parts: (a) the hydrostatics provide restoring force in heave, roll and pitch; (b) the mooring lines provide the restoring force which are represented here by nonlinear horizontal; and (c) vertical springs. An unidirectional regular wave model is used for computing the incident wave kinematics by Airy’s wave theory and force by Morison’s equation. The response analysis is performed in time domain to solve the dynamic behavior of a moored Spar platform as an integrated system using the iterative incremental Newmark’s Beta approach. Numerical studies are conducted for several regular waves.

Background: The epidemiology of heart failure in Arabia, with a population different from the West in cultural and ethnic origin, has not been studied before. Aims: To determine the prevalence and aetiologies of symptomatic heart failure in an indigenous Arab population over a 3-year period. Methods: All patients with heart failure ≥ 13 years of age, treated at the only secondary care hospital of the Dhakliya region of Oman between 1992 and 1994 were evaluated prospectively by clinical history and physical examination. Chest radiograph and echo-Doppler studies were used to confirm the diagnosis of heart failure. Exercise stress testing and/or coronary angiography were also performed in patients > 30 years of age, or earlier if ischaemic heart disease was suspected. Results: A total of 1164 patients were identified giving a prevalence of 5.17/1000 population during the study period (6.04/1000 among males and 4.21/1000 among females; P < 0.001). The prevalence increased with age from 1.05 / 1000 in age group < 45 years to 15.7/1000 in 45–64 years (P < 0.001) and 25.2 / 1000 in ≥ 65 years (P < 0.001). Common causes of heart failure were ischaemic heart disease (51.7%), hypertensive heart disease (24.9%) and idiopathic dilated cardiomyopathy (8.3%). Valvular heart disease and lung diseases causing heart failure were less common. Conclusion: The prevalence of symptomatic heart failure was appreciably significant in the population studied, showed a male preponderance and was frequent in people aged ≥ 45 years. Ischaemic heart disease and hypertension were the commonest aetiologies but idiopathic dilated cardiomyopathy was also present in a significant number of patients being relatively more prevalent than reported from the West.

Dilated cardiomyopathy (DCM) is an important cause of chronic congestive cardiac failure (CCF) in infants and children. Although a variety of aetiological factors have been listed, most patients with echocardiographically documented DCM do not possess a demonstrable cause. Poor myocardial function in DCM triggers a sequence of compensatory mechanisms, mediated through the renin angiotensin system, the sympathetic system (neural and humoral) and a number of vasodilatory molecules. These favour myocardial and peripheral vascular remodelling by necrosis, fibrosis and apoptosis which ultimately does more harm than good. Management is essentially similar to that of CCF using a combination of diuretics, angiotensin converting enzyme inhibitors (ACEI) and digoxin. Use of additional diuretics, intravenous frusemide, dobutamine infusion and β-adrenergic receptor blockers help to improve quality of life in resistant patients. ACEI, β-adrenergic blockers and possibly aldosterone antagonists prolong survival. Compliance to medication can be enhanced by improving drug formulations and by assisting the family to choose the ‘best-fit’ regimen (concordance). At present, optimum management of end-stage CCF is cardiac transplant. Conclusion Current understanding of the pathophysiology of chronic congestive cardiac failure resulting from dilated cardiomyopathy has shifted management strategy from steps that directly improve myocardial function to those that modulate the neuroendocrine profile and peripheral vascular reactivity. Similar advances in therapeutic applications would be assisted by controlled studies and full licensing of drugs for use in children. Medical intervention will remain the cornerstone of management until advances in surgical techniques become more widely available.

Background: Awareness of prevalence, determinants, and prognosis of asymptomatic untreated prehypertension is still lacking especially in India and subcontinent. Aim: The present study was to assess the effects of prehypertension on structure, function and geometrical pattern of left ventricle on the basis of left ventricular mass (LVM), left ventricular mass indexed to height (LVMI/Ht), and relative wall thickness (RWT) recorded by echocardiography based on the American society of echocardiography (ASE) convention. Methods: The study population included prehypertensives (n 61; 31 M, 30 F) and normotensives (n 38; 19 M, 19 F) between age 25 and 65 years, and were assessed by echocardiography. Results: It was observed that the stroke volume (SV), cardiac output (CO), cardiac index (CI), body mass index (BMI), body surface area (BSA), were found to be little elevated but was not significant in hypertensive females compared to normotensives. Systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate (HR), pulse pressure (PP), mean arterial pressure (MAP), end systolic stress (ESS), and end isovolumetric systolic stress (EISS) were significantly elevated (p

We propose modified random early detection (MRED) gateways for congestion avoidance in TCP/IP networks. MRED aims at providing better control over the burstiness level while remaining the advantages of RED. We use ns2 to simulate a series of network configurations and the numerical results demonstrate that MRED can achieve higher link utilization compared to RED without sacrificing its advantages in all simulation scenarios. The improvement becomes more significant under bursty traffic.

We report an unusual case in which a 28-year-old woman presented with a long-standing history of ear discharge, hearing loss, facial weakness with ipsilateral facial swelling and cellulitis, a postauricular fistula, and an abscess of the temporozygomatic, infratemporal, and parotid areas. The pus stained positive for bacteria and acid-fast bacilli, and culture was positive for Proteus vulgaris and mycobacteria. Based on these findings, a diagnosis of tuberculous otitis media with complications was made. Computed tomography showed extensive destruction of the tympanic and mastoid part of the temporal bone, as well as lytic lesions in the skull. The patient was placed on antituberculosis drug therapy. Although her facial nerve palsy and hearing loss persisted, she otherwise responded well and did not require surgery.

Telecommunication (telco) systems for telephony, video, and other broadband services will use a large number of fiber optic connectors and many of these connectors may be deployed in the outside plant (OSP). To meet telco plant expectations, these connectors must maintain their performance for at least 15-20 years. Are the available fiber optic connector designs capable of meeting these requirements? Is there a concern about connector performance or reliability? To answer these questions and develop some understanding of the behavior of fiber optic connectors in the OSP environment, SC type connectors from four manufacturers were evaluated by subjecting them to a sequence of tests simulating OSP conditions. This paper presents the results of the environmental tests. >

The high-temperature operation of a silicon carbide gate turn-off thyristor is evaluated for use in inductively loaded switching circuits. Compared to purely resistive load elements, inductive loads subject the switching device to higher internal power dissipation. The ability of silicon carbide components to operate at elevated temperatures and high power dissipations are important factors for their use in future power conversion/control systems. In this work, a maximum current density of 540 A/cm/sup 2/ at 600 V was switched at a frequency of 2 kHz and at several case temperatures up to 150/spl deg/C. The turn-off and turn-on characteristics of the thyristor are discussed.

We present the case report of a 10-year-old girl who presented to us with a painless swelling involving the left infraorbital region. The swelling was diagnosed to be tubercular in origin with erosion of the zygomatic, maxillary and frontal bones constituting the inferior and lateral walls of the left orbit. The patient responded well to antitubercular chemotherapy. A discussion of the case and a literature review of causes of orbital erosion is presented.

For a preliminary inversion of magnetotelluric (MT) data obtained in continental regions it is common practice to assume initially that the underlying structure is one dimensional (ID) so that one of the readily available routines for simple ID inversion may be applied. If the continental structure is actually 2D, as is often the case, such approximate inversions may lead to different conclusions depending on whether transverse electric (TE) or transverse magnetic (TM) data are used, and for this reason rotationally invariant impedances (the ‘Berdichevsky average’ or the ‘effective impedance’) are sometimes preferred in practice. When the composite 2D model obtained by applying these inversions at different sites in an array is used as a starting model for optimizing the fit between model and observed responses, it is desirable that all significant structural features are included in it. With this is mind, the effectiveness of the TE, TM and rotationally invariant impedances in yielding meaningful 1D inversions in a 2D environment is tested by studying various basic models (horst, resistive and conductive blocks alone and together, surface conducting edge and conducting sill) with the aid of a new 2D finite difference program and a recently developed automatic scheme for 1D inversion. The paper concludes with the construction of a 2D structure from the real COPROD2R data using as a starting model the layered models obtained from separate 1D inversions at various MT sites in the array, and then optimizing the least-squares fit of both the TE and TM model responses to the observed responses by adjusting the parameters of the initial model. The North American Central Plains Anomaly beneath a shallow sedimentary cover is identified by this procedure in the form of two upright and adjacent conductive blocks; this differs somewhat from some previously proposed models but yields a good fit to the apparent resistivity and phase responses at 20 sites.

The spatial dependence of the characteristic periods (Tc) of the induction arrows along a profile over a conductive plate-resistive host is investigated for two dimensional numerical models of a conductive plate of (i) semi-infinite and (ii) finite widths in uniform and layered resistive hosts. Induction arrows are computed for a large period range (2–25 600 s) at selected distances on either side of the conductive-resistive interface, and empirical curves for the characteristic period (period at which the quadrature induction arrow reverses sign) as a function of distance from the interface are presented. The characteristic period is seen to have a minimum value at the interface and then to increase with distance from the interface both over the conductive plate and the resistive host. The characteristic period at a given point on either side of the interface is also seen to increase with increasing depth of the conductive substratum. For the case of a finite width plate, a minimum in Tc is observed at both plate boundaries. The characteristic periods at the interface, and at points on either side of the interface, are found generally to depend on the conductivities of the plate and host, the depth of burial and dimensions of the plate, and the depth of the conductive substratum. The results show that the characteristic periods at sites along a profile over a 2-D conductive body could, in principle, be used to delineate the location of the conductive-resistive interface, and provide information on the dimensions, depth of burial, and the conductivity of the conductive body in a host earth if the conductivity of the host and substratum were known.

A single-phase-to-three-phase cycloconverter system operating from a 50 Hz input has been simulated under various loading conditions using a PSPICE circuit simulator. The Giacolleto SCR model has been modified. Detailed waveforms of load voltage, load current, and current of various semiconductor-controlled rectifiers (SCRs) have been plotted. It has been demonstrated that for low and medium L/R loads a simple constant firing angle sequence works well, whereas the cosine wave crossing method (CWCM) seems to be optimum for high L/R loads. Theoretical results are validated with the experimental results. >

This paper examines the performance of wireless mesh networks (WMNs) under the impact of path-based denial of service (DoS) attacks. Specifically, we study the factors that are conducive to path-based DoS attacks, while focusing external interferences, medium errors, and physical diversity. We setup a wireless mesh testbed and configure a set of experiments to gather measurements and assess the effects of different factors. We find that the impact of external interferences and medium errors on network performance is exacerbated when path-based DoS attacks are carried out. Another interesting observation is that a far attacker can lead to an increased performance degradation than a close-by attacker due to physical diversity. Further, we discuss a simple strategy to counter path-based DoS attacks, which has potential for reducing the impact of the attack significantly.

Un tabique nasal desviado esta asociado con una hipertrofia compensatoria de la concha nasal inferior del lado contra lateral. En el pasado se realizaba septoplastia convencional para el tabique desviado, lo que mejoraraba la permeabilidad en el lado de la desviacion, pero agravaba esta en el lado opuesto, debido a la reacomodacion del tabique en el plano mediano. En el presente estudio se evaluo en 50 pacientes la composicion anatomica de las conchas nasales inferiores, basado en la exploracion a traves de tomografia computarizada, y de esta manera ayudar al otorrinolaringologo a determinar si es necesario o no, anadir la plastia de la concha nasal inferior al procedimiento de septoplastia estandar.

Justification is given for using the word ‘vector’ (with its mathematical implications) to describe the arrows first employed by Parkinson and Wiese to depict induced magnetic variation fields associated with conductivity anomalies. Despite this, caution should be exercised when trying to interpret physically the resultant obtained by adding or subtracting such vectors. Induction in a rectangular surface anomaly near a coastline is investigated numerically with the aid of a thin sheet program for inducing fields of periods 1 h and 20 min. It is found that in certain regions the induction vectors for this configuration are not given by the resultants of the separate induction vectors for the coastline and anomaly alone unless the anomaly is so far removed from the coastline that there is little electromagnetic coupling between them.

SiC semiconductor devices are becoming more common in high power applications. This is largely due to higher blocking voltages and faster switching speeds. The development of SiC devices, specifically thyristors and GTOs, is still an evolving process [1]. There is not yet a single device capable of handling the magnitude of current typically seen in transmission and distribution systems and as a result these devices must be paralleled into a single switching position. SiC thyristors were used to carry out a study on paralleled SiC bipolar devices. Si bipolar devices are much better matched than SiC devices, but they exhibit much slower turn-on times [2]. Thus, the most suitable method of inducing current sharing in these devices is through gate control. However, SiC devices exhibit fast turn-on times while being poorly matched. Using various methods of gate control for SiC bipolar devices in parallel does not significantly affect the current sharing. The best way to improve current sharing is obtained using series resistors. These resistors should be chosen so that the voltage drop and power losses are minimized. The effects of thermal runaway are observed as well. As a device rises in temperature relative to the other devices, it conducts more current due to its negative temperature coefficient of on-state resistance. In order to maintain proper heat sharing, a design for a package is presented that includes three thyristors in parallel on a common substrate.

The effect of a coastline on geomagnetic variations associated with the daytime equatorial electrojet for Sq (24 h) and substorm (20 and 60 min) periods has been investigated with the aid of a thin sheet algorithm developed at the University of Victoria. The numerical model comprises a thin sheet at the surface of and electrically connected to a two-layer structure representing a 30 km thick crust of conductivity 0.005 S m −1 and an underlying mantle of conductivity 0.1 S m −1 . The sheet includes lateral variations of conductance corresponding to a land-sea interface: (1) parallel to, (2) perpendicular to and (3) inclined at an angle to the dip-equator. The electrojet is represented by a gaussian distribution of ionospheric currents flowing eastwards, of half-width (standard deviation) 150 km, both with and without the inclusion of northern and southern return current flows. It is found that even at Sq periods, anomalies in the northward horizontal and vertical components of the magnetic field, H and Z respectively, are apparent for the electrojet source without return currents. The effects are less when return currents are included in the external source field. Anomalies in the eastward horizontal component D for both types of sources are very small except near the periphery of the jet, where they become significant ( > 2 nT) when the coastline is perpendicular to the dip-equator. The computed value of the ratio of internal to external parts of H for the electrojet source without return currents is 0.24 near the centre of the electrojet, regardless of the direction of the coastline, which is in close agreement with the value 0.28 obtained from rocket and ground data. Changing, the half-width of the electrojet from 50 to 300 km caused the ratio to vary between 0.14 and 0.34. The induced effects are found to be more prominent at substorm periods than for the longer-period Sq variation and they are highly dependent on the strike of conductivity contrast.

Two-dimensional numerical model calculations, employing a finite difference technique, are used to study the behaviour of the induction arrows, for a range of periods, for a conductive plate of (i) semi-infinite and (ii) finite width in uniform and layered resistive hosts. The results for the conductive plate at the surface of the host have application to a uniform-depth ocean, while the results for the plate buried at some depth in the resistive host have application to a conductive sill in a resistive Earth. The numerical results indicate that for a profile over the plate-host vertical interface the in-phase arrows for all periods and locations point towards the conductive plate, while the quadrature arrows at periods near the characteristic period of the model are oppositely directed on either side of the interface so as to point towards each other and towards the interface for nearby locations, both over the conductive plate and the resistive host. Further, the quadrature arrow undergoes a second reversal over the resistive host at a distance from the interface that is somewhat dependent on the period. Thus, at either side of the location of this second reversal, the quadrature induction arrows are again oppositely directed, but pointing away from each other, with the arrows near the interface pointing towards, and the more distant arrows pointing away from the conductive plate. The period range for the quadrature-arrow reversal is characteristic of conductivities and layer depths. The features of the quadrature-arrow sign reversals at and near the interface are in accordance with the earlier laboratory analogue model results of Hebert et al. for the Newfoundland coastal region and Nienaber et al. for a conductive plate in a resistive host. It is suggested that in practice the sign reversal of the quadrature arrow may aid in locating a conductor-host interface, and that if the conductivity of the host is known, the maximum in the anomalous vertical magnetic field response may permit an approximate determination of the conductive-layer depth.

The induction effect on geomagnetic variations due to the daytime electrojet in the region of the Indian peninsula and Sri Lanka has been investigated numerically with the aid of a thin sheet algorithm. The electrojet is represented by a Gaussian current distribution over a band of about 600 km width with its maximum intensity close to the dip-equator and a height of 110 km. An inducing source comprising an equatorial electrojet superimposed on the uniform planetary field is also considered. The results are presented in the form of contour plots and the differences between the magnetic field components associated with electrojet and uniform sources are highlighted. It is observed that the non-uniformity of the source in daytime events has a profound effect on the induced currents in the region. The dual effect of reduced current intensity and opposing external and internal parts results in smaller vertical magnetic field variations over the southern peninsula especially close to the periphery of the electrojet. It is confirmed that for a pure electrojet source the vertical field vanishes completely in the region of the permanent geomagnetic station at Annamalainagar thereby lending credence to a recently proposed method of separating a daytime magnetic event into its ionospheric and magnetospheric parts. An examination of field ratios shows that the magnetotelluric impedance is less dependent on the source effect over the whole region than other parameters. Finally, it is shown that in the presence of a combined electrojet and uniform source field, the observed equatorial enhancement is not proportional to the strength of the electrojet alone but is also critically dependent on the intensity of the uniform part of the field.

Wireless Local Area Networks (WLANs) are vulnerable to malicious attacks due to their open shared medium. Consequently, provisioning enhanced security with strong cryptographic features and low performance overhead becomes exceedingly necessary to actualize real-time services in WLANs. In order to exploit full advantage of existing security protocols at various layers, we study the cross-layer interactions of security protocols in WLANs under different network scenarios. In particular, we present a detailed experimental study on the integration of commonly used security protocols such as WEP, 802. lx and EAP, IPsec and RADIUS. First, we classify individual and hybrid policies, and then, define security index and cost functions to analyze security strength and overhead, quantitatively, of each policy. By setting-up an experimental testbed, we measure performance cost of various policies in terms of authentication time, cryptographic cost and throughput using TCP/UDP traffic streams. Our results demonstrate that in general, the stronger the security, the more signaling and delay overhead, whereas, the overhead does not necessarily increase monotonically with the security strength. Therefore, it is suggested to provide substantial security at a reasonable cost of overhead with respect to mobile scenarios and traffic streams. Also, we notice that authentication time will be a more significant factor contributing towards QoS degradation than cryptographic cost, which is critical to real-time service in wireless networks.

Distributed network-control-systems (D-NCS) are a network structure and components that are capable of integrating sensors, actuators, communication, and control algorithms to suit real-time applications. They have been gaining popularity due to their high potential in widespread applications and becoming realizable due to the rapid advancements in embedded systems, wireless communication and data transfer technologies. This paper addresses the issue of D-NCS information security as well its time-sensitive performance with respect to network security schemes. We use a wireless network based, robot navigation path tracking system called Intelligent Space (iSpace) as a D-NCS test bed in this paper. The paper classifies the delay data from every NCS module (sensors, actuators and controllers). We define performance parameters for this NCS test bed. Various system factors including network delay, system gain, affecting these performance parameters are recognized. Network security algorithms DES and 3DES are integrated with the application to secure the sensitive information flow. Standard statistical approach such as 2k factorial experiment design, analysis of variance, hypothesis testing is used to study and estimate the effect of each factor on the system performance especially security features. Thorough experimental results, tables of detailed characterization and effect estimate analysis is presented followed by the discussion on the performance comparison of NCS with and without wireless security.

Radio links exhibit highly unpredictable properties such as variable bandwidth and bit error rates that affect the performance of applications in wireless networks. Besides, another critical concern is the protection of applications due to shared and open wireless medium. However, protection services add additional performance overhead to carry out their operations, and incur varying effects on the network performance, depending on link characteristics. Thus, how to provide protected and high performance service is a challenging issue in wireless networks. The problem is even more challenging for real-time applications such as voice over IP (VoIP) with stringent delay and packet loss requirements. In this paper, we present a novel approach to improve application performance by implementing Link Aware Protection (LAP) in wireless local area networks (LANs). LAP exploits dynamic security policy management (DSPM) scheme for adapting protection with varying link quality. We present a real-time implementation of LAP in our wireless LAN testbed. As a case study, we demonstrate VoIP performance on our LAP enabled wireless clients. The results show the possibility of maintaining an adequate protection and achieving improved performance for VoIP streams under link variations.

Summary form only given. The U.S. Army Research Laboratory is evaluating silicon carbide semiconductor components to determine the range of high power and pulsed power applications for which SiC is a sensible material to use. With SiC's tolerances for high temperatures and high current densities, compact modules of SiC diodes might be ideal for protecting other high power circuit components under pulse conditions. This study evaluated SiC diodes with a footprint of 0.73 cm2 which were designed bv Cree, Inc. and packaged and pulse tested at ARL. The diodes are rated for 6 kV blocking and 50 A of continuous forward current. They were arranged to clamp reverse currents at the switching end of a large capacitor bank and were pulsed at a single shot rate both individually and in parallel. Individual diodes were pulsed as high as 5.9 kA (corresponding to an action of 4.5 times 103 A2s) for 25 single shots before failing, and as high as 5.0 kA (with an action of 3.5 times 103 A2s) for over 100 shots without failure. Groups of diodes were characterized on a curve tracer and matched based on on-state dV/dl slope, which ranged from 3.7-4.0 mOmega. Five diodes paralleled in the pulse testbed carried a total current of 23 kA with each diode sharing 19-21% of the total peak current. Modules consisting of 8-10 diodes in parallel will be similarly pulsed to reach a peak total current of 40 kA and will ultimately be combined in a single, compact package for higher current applications.

Distributed network-control-systems (D-NCS) are a multidisciplinary effort whose aim is to produce a network structure and components that are capable of integrating sensors, actuators, communication, and control algorithms in a manner to suit real-time applications. They have been gaining popularity due to their high potential in widespread applications and becoming more realizable due to the rapid advancements in wireless communication and data transfer technologies. This paper addresses the issue of D-NCS information security as well its real-time performance with respect to network security protocols and encryption schemes. We use a wireless network based, robot navigation path tracking system called intelligent space (iSpace) as a D-NCS test bed in this paper. The paper classifies the data from every NCS module (sensors, actuators and controllers) according to bandwidth requirement, time and information sensitivity. We define performance parameters for this NCS test bed. Various system factors affecting these performance parameters are recognized. Network security algorithms DES and 3DES are integrated with the application to encrypt the sensitive information flow. These wireless security features are considered as an added factor to the NCS. Standard statistical approach (2k factorial experiment design) is used to study and estimate the effect of each factor on the system performance especially security additions. Thorough experimental results, tables of detailed characterization and effect estimate analysis is presented followed by the discussion on the performance comparison of NCS with and without wireless security.

Distributed networked-controlled-systems (NCS) are a multidisciplinary effort whose aim is to produce a network structure and components that are capable of integrating sensors, actuators, communication, and control algorithms in a manner to suit real-time applications. They have been very popular and widely applied for many years now due to the rapid advancements in data and communication wireless technologies. There are many challenges to be overcome in order to put such a heterogeneous system together. Key issues to be considered are network delay, data sensitivity and information security. This paper characterizes a wireless distributed NCS, a testbed called iSpace based on these key factors. We integrated static network security algorithms DES and 3DES with the NCS testbed iSpace - a multidisciplinary network based robot navigation system - and characterized it on the basis of bandwidth requirement, data classification and data sensitivity, network delay effect on the system performance. The paper demonstrates through results that a dynamic optimization is required between network security for reliability and time-sensitivity of the NCS. Future work in dynamic optimization in security is suggested.

Performance degradation due to routing overhead is a serious impediment to fulfilling quality of service (QoS) in mobile ad hoc networks (MANETs). Therefore, analyzing the impact of routing overhead in a real-time environment becomes critical to developing efficient routing protocols and provisioning network performance. We develop a statistical-analytic approach to studying the impact of the routing overhead on delay and throughput in a real-time MANET testbed. The approach helps us in deriving statistical models of delay and throughput which, in turn, enables us to analyze the behavior of routing protocols beyond the scenarios configured in the testbed. In addition, we conduct a simple analysis of measuring network bandwidth consumed by routing overhead in various environments. Although optimized link state routing (OLSR) and ad-hoc on-demand distance vector (AODV) routing protocols are investigated as case studies in this paper, our approach and findings are applicable to other routing protocols as well.

Military wireless networks suffer from privacy and performance concerns due to their shared radio medium and off-the-shelf products. Therefore, robust and efficient security management is essential in these networks, especially for the transmission of sensitive data. However, security solutions based on static-configuration paradigm do not adapt to changing network conditions, such as variations in wireless link characteristics, leading to degradation in system performance. The rationale for advocating dynamic security paradigm is to achieve optimized network performance and security based on network conditions. Therefore, we propose a dynamic security policy management (DSPM) in which security policies can be changed on the fly based on the network feedback about wireless link conditions. DSPM is analyzed by using semi-Markov decision process to determine the optimal instances for switching security policies. The results show that DSPM provides enhanced security and improved performance than static security.

In this paper, we study and quantify the impact of the most widely used security protocols, such as 802.1x, EAP, IPSEC, SSL and RADIUS, in wireless local area networks (WLANs). Based on the measurements in a wireless network testbed, we present quantitative, realistic findings with regards to both security functions as well as network performance. First, we describe experimental setup including system configuration and protocol stack. Then, we consider a variety of individual and hybrid security policies in order to capture the impact of security services at different network layers. Moreover, depending upon mobile nodes' current location, user mobility is categorized into non-roaming and roaming scenarios. In addition, we define several performance metrics such as authentication time, authentication messages, response time, throughput to measure the overhead associated with security policies on system performance. Comprehensive experimental measurements and analysis are provided for TCP/UDP traffic streams and network variations to demonstrate the impact of security protocols in WLANs.

Fast neutron response measurements are reported for radiation detectors based on large-volume SiC p-i-n diodes. Multiple reaction peaks are observed for 14-MeV neutron reactions with the silicon and carbon nuclides in the SiC detector. A high degree of linearity is observed for the /sup 28/Si(n,/spl alpha//sub 1/) reaction set of six energy levels in the product /sup 25/Mg nucleus, and pulse height defect differences between the observed /sup 12/C(n,/spl alpha//sub 0/) and /sup 28/Si(n,/spl alpha//sub 1/) energy responses are discussed. Energy spectrometry applications in fission and fusion neutron fields are also discussed.