Showing papers by "University of California published in 2002"

CIL: Intermediate Language and Tools for Analysis and Transformation of C Programs

Abstract: This paper describes the C Intermediate Language: a high-level representation along with a set of tools that permit easy analysis and source-to-source transformation of C programs.Compared to C, CIL has fewer constructs. It breaks down certain complicated constructs of C into simpler ones, and thus it works at a lower level than abstract-syntax trees. But CIL is also more high-level than typical intermediate languages (e.g., three-address code) designed for compilation. As a result, what we have is a representation that makes it easy to analyze and manipulate C programs, and emit them in a form that resembles the original source. Moreover, it comes with a front-end that translates to CIL not only ANSI C programs but also those using Microsoft C or GNU C extensions.We describe the structure of CIL with a focus on how it disambiguates those features of C that we found to be most confusing for program analysis and transformation. We also describe a whole-program merger based on structural type equality, allowing a complete project to be viewed as a single compilation unit. As a representative application of CIL, we show a transformation aimed at making code immune to stack-smashing attacks. We are currently using CIL as part of a system that analyzes and instruments C programs with run-time checks to ensure type safety. CIL has served us very well in this project, and we believe it can usefully be applied in other situations as well.

Erasure Coding Vs. Replication: A Quantitative Comparison

Abstract: Peer-to-peer systems are positioned to take advantage of gains in network bandwidth, storage capacity, and computational resources to provide long-term durable storage infrastructures. In this paper, we quantitatively compare building a distributed storage infrastructure that is self-repairing and resilient to faults using either a replicated system or an erasure-resilient system. We show that systems employing erasure codes have mean time to failures many orders of magnitude higher than replicated systems with similar storage and bandwidth requirements. More importantly, erasure-resilient systems use an order of magnitude less bandwidth and storage to provide similar system durability as replicated systems.

Patterns of brain atrophy in frontotemporal dementia and semantic dementia.

Abstract: Objective: To identify and compare the patterns of cerebral atrophy associated with two clinical variants of frontotemporal lobar degeneration (FTLD): frontotemporal dementia (FTD) and semantic dementia (SemD). Methods: Twenty patients with FTLD were classified as having FTD (N = 8) or SemD (N = 12) based on current clinical criteria. Both groups showed a similar spectrum of behavioral abnormalities, as indicated by the neuropsychiatric inventory. T1-weighted MRI was obtained for each patient and 20 control subjects. The regions of focal gray matter tissue loss associated with both FTD and SemD, as well as those differing between the two groups were examined using voxel-based morphometry. Results: Regions of significant atrophy seen in both groups were located in the ventromedial frontal cortex, the posterior orbital frontal regions bilaterally, the insula bilaterally, and the left anterior cingulate cortex. The FTD, but not the SemD, group showed atrophy in the right dorsolateral frontal cortex and the left premotor cortex. The SemD, but not the FTD, group showed tissue loss in the anterior temporal cortex and the amygdala/anterior hippocampal region bilaterally. Conclusions: Although FTD and SemD are associated with different overall patterns of brain atrophy, regions of gray matter tissue loss in the orbital frontal, insular, and anterior cingulate regions are present in both groups. The authors suggest that pathology in the areas of atrophy associated with both FTD and SemD may underlie some the behavioral symptoms seen in the two disorders.

Device and method for forming a circumferential conduction block in a pulmonary vein

Abstract: This invention is a method for treating a patient diagnosed with atrial arrhythmia by forming a circumferential conduction block along a circumferential path of tissue in a pulmonary vein wall that circumscribes the pulmonary vein lumen and transects the electrical conductivity of the pulmonary vein such that conduction is blocked along the longitudinal axis of the vein wall and into the left atrial wall. The method is performed to treat a patient with a focal arrythmogenic origin along the pulmonary vein wall by either ablating the focal origin or by isolating the focal origin from the atrial wall with the circumferential conduction block. The circumferential conduction block is also formed in a pulmonary vein in order to bridge the adjacent ends of two linear lesions, wherein each linear lesion is formed to extend between the pulmonary vein and another adjacent pulmonary vein in a less-invasive “maze”-type procedure. A circumferential ablation element in a circumferential ablation device assembly is used in a percutaneous translumenal catheter technique in order to form the circumferential conduction block in the pulmonary vein wall.

OSIRIS: A Three-Dimensional, Fully Relativistic Particle in Cell Code for Modeling Plasma Based Accelerators

Abstract: We describe OSIRIS, a three-dimensional, relativistic, massively parallel, object oriented particle-in-cell code for modeling plasma based accelerators. Developed in Fortran 90, the code runs on multiple platforms (Cray T3E, IBM SP, Mac clusters) and can be easily ported to new ones. Details on the code's capabilities are given. We discuss the object-oriented design of the code, the encapsulation of system dependent code and the parallelization of the algorithms involved. We also discuss the implementation of communications as a boundary condition problem and other key characteristics of the code, such as the moving window, open-space and thermal bath boundaries, arbitrary domain decomposition, 2D (cartesian and cylindric) and 3D simulation modes, electron sub-cycling, energy conservation and particle and field diagnostics. Finally results from three-dimensional simulations of particle and laser wakefield accelerators are presented, in connection with the data analysis and visualization infrastructure developed to post-process the scalar and vector results from PIC simulations.

Organo luminescent semiconductor nanocrystal probes for biological applications and process for making and using such probes

Abstract: A semiconductor nanocrystal compound is described capable of linking to an affinity molecule. The compound comprises (1) a semiconductor nanocrystal capable of emitting electromagnetic radiation and/or absorbing energy, and/or scattering or diffracting electromagnetic radiation—when excited by an electromagnetic radiation source or a particle beam; and (2) at least one linking agent, having a first portion linked to the semiconductor nanocrystal and a second portion capable of linking to an affinity molecule. The compound is linked to an affinity molecule to form a semiconductor nanocrystal probe capable of bonding with a detectable substance. subsequent exposure to excitation energy will excite the semiconductor nanocrystal in the probe causing the emission of electromagnetic radiation. Further described are processes for respectively: making the luminescent semiconductor nanocrystal compound; making the semiconductor nanocrystal probe; and using the probe to determine the presence of a detectable substance in a material.

Methods of fabricating nanostructures and nanowires and devices fabricated therefrom

Abstract: One-dimensional nanostructures having uniform diameters of less than approximately 200 nm. These inventive nanostructures, which we refer to as “nanowires”, include single-crystalline homostructures as well as heterostructures of at least two single-crystalline materials having different chemical compositions. Because single-crystalline materials are used to form the heterostructure, the resultant heterostructure will be single-crystalline as well. The nanowire heterostructures are generally based on a semiconducting wire wherein the doping and composition are controlled in either the longitudinal or radial directions, or in both directions, to yield a wire that comprises different materials. Examples of resulting nanowire heterostructures include a longitudinal heterostructure nanowire (LOHN) and a coaxial heterostructure nanowire (COHN).

Global Impact of Salinity and Agricultural Ecosystems

Abstract: Agricultural losses caused by salinity are difficult to assess but estimated to be substantial and expected to increase with time. Secondary salinization of agricultural lands is particularly widespread in arid and semiarid environments where crop production requires irrigation chemes. At least 20% of all irrigated lands are salt-affected, with some estimates being as high as 50%. Whereas the world’s population continues to rise, the total land area under irrigation appears to have leveled off. The need for increased food production therefore needs to be met by increases in yield per land area. To reach this goal, genetic engineering of crop plants for enhanced salt tolerance will be a very important approach. In dry regions where fresh water becomes a scarce commodity, irrigation of moderately salt tolerant crops with brackish water is feasible. Transgenic lines of some crop species have been generated which can grow and develop at fairly high salinity levels in controlled environments. These transgenics must be tested vigorously for yield potential under field conditions.

The Dodo Bird Verdict Is Alive and Well—Mostly

Abstract: We examined 17 meta-analyses of comparisons of active treatments with each other, in contrast to the more usual comparisons of active treatments with controls. These meta-analyses yielded a mean uncorrected absolute effect size for Cohen's d of .20, which is small and non-significant (an equivalent Pearson's r would be. 10). The smallness of this effect size confirms Rosenzweig's supposition in 1936 about the likely results of such comparisons. In the present sample, when such differences were corrected for the therapeutic allegiance of the researchers involved in comparing the different psychotherapies, these differences tend to become even further reduced in size and significance, as shown previously by Luborsky, Diguer, Seligman, et al. (1999).

Tissue ablation device and method of use

Abstract: A tissue ablation device creates long linear lesions along a body space wall of an animal, and primarily between adjacent pulmonary vein ostia in a left atrial wall. An ablation element includes first and second ends that are bordered by first and second anchors. The anchors are adapted to secure the ablation element ends at predetermined first and second locations along the body space wall such that the ablation element is adapted to ablate an elongate region of tissue between those locations. The anchors may be guidewire tracking members, each including a bore adapted to receive and track over a guidewire, and may anchor within adjacent pulmonary vein ostia when the engaged guidewires are positioned within the respective veins. Stop members may be provided on the guidewires and may be adapted for positioning the relative anchors or for forcing the anchors to fit snugly within the vein ostia. A conduit passageway through the catheter houses a stiffening stylet which may be advanced into the region of the ablation element in order to impart a shape to that element to conform it to a predetermined region of anatomy, or to stiffen the underlying catheter in order to advance the assembly into remote anatomy.

Host multicast: a framework for delivering multicast to end users

Abstract: While the advantages of multicast delivery over multiple unicast deliveries is undeniable, the deployment of the IP multicast protocol has been limited to "islands" of network domains under single administrative control. Deployment of inter-domain multicast delivery has been slow due to both technical and administrative reasons. In this paper we propose a Host Multicast Tree Protocol (HMTP) that (1) automates the interconnection of IP-multicast enabled islands and (2) provides multicast delivery to end hosts where IP multicast is not available. With HMTP, end-hosts and proxy gateways of IP multicast-enabled islands can dynamically create shared multicast trees across different islands. Members of an HMTP multicast group self-organize into an efficient, scalable and robust multicast tree. The tree structure is adjusted periodically to accommodate changes in group membership and network topology. Simulation results show that the multicast tree has low cost, and data delivered over it experiences moderately low latency.

Black-Box Analysis of the Block-Cipher-Based Hash-Function Constructions from PGV

Abstract: Preneel, Govaerts, and Vandewalle [6] considered the 64 most basic ways to construct a hash function H: {0, 1}* ? {0, 1}n from a block cipher E: {0, 1}n × {0, 1}n ? {0, 1}n. They regarded 12 of these 64 schemes as secure, though no proofs or formal claims were given. The remaining 52 schemes were shown to be subject to various attacks. Here we provide a formal and quantitative treatment of the 64 constructions considered by PGV. We prove that, in a black-box model, the 12 schemes that PGV singled out as secure really are secure: we give tight upper and lower bounds on their collision resistance. Furthermore, by stepping outside of the Merkle-Damgard approach to analysis, we show that an additional 8 of the 64 schemes are just as collision resistant (up to a small constant) as the first group of schemes. Nonetheless, we are able to differentiate among the 20 collision-resistant schemes by bounding their security as one-way functions. We suggest that proving black-box bounds, of the style given here, is a feasible and useful step for understanding the security of any block-cipher-based hash-function construction.

GQ and Schnorr Identification Schemes: Proofs of Security against Impersonation under Active and Concurrent Attacks

Abstract: The Guillou-Quisquater (GQ) and Schnorr identification schemes are amongst the most efficient and best-known Fiat-Shamir follow-ons, but the question of whether they can be proven secure against impersonation under active attack has remained open. This paper provides such a proof for GQ based on the assumed security of RSA under one more inversion, an extension of the usual one-wayness assumption that was introduced in [5]. It also provides such a proof for the Schnorr scheme based on a corresponding discrete-log related assumption. These are the first security proofs for these schemes under assumptions related to the underlying one-way functions. Both results extend to establish security against impersonation under concurrent attack.

Motor sequence learning with the nondominant left hand. A PET functional imaging study.

Abstract: Whereas the human right hemisphere is active during execution of contralateral hand movements, the left hemisphere is engaged for both contra- and ipsilateral movements, at least for right-handed subjects. Whether this asymmetry is also found during motor learning remains unknown. Implicit sequence learning by the nondominant left hand was examined with the serial reaction time (SRT) task during functional brain imaging. As learning progressed, increases in brain activity were observed in left lateral premotor cortex (PMC) and bilaterally in supplementary motor areas (SMA), with the increase significantly greater in the left hemisphere. The left SMA site was similar to one previously identified with right-hand learning, suggesting that this region is critical for representing a sequence independent of effector. Learning with the left hand also recruited a widespread set of temporal and frontal regions, suggesting that motor skill learning with the nondominant hand develops within both cognitive and motor-related functional networks. After skill acquisition, subjects performed the SRT task with their right hands, and sequence transfer was tested with the original and a mirror-ordered sequence. With the original sequence, the stimulus sequence and series of response locations remained unchanged, but the finger movements were different. With the mirror-ordered sequence, the response sequence involved finger movements homologous to those used during training. Performance of the original and mirror sequence by the right hand was significantly better than with random stimuli. Mirror transformation of the sequence by the right hand was associated with a marked increase in regional activity in the left motor cortex, consistent with a role for sequential transformation at this level of the motor output pathway.

Group-iii nitride based high electron mobility transistor (hemt) with barrier/spacer layer

Abstract: A group III nitride based high electron mobility transistor (HEMT) (10) is disclosed that provides improved high frequency performance. One embodiment of the HEMT (10) comprises a GaN buffer layer (26), with an AlyGa1-yN (y=1 or y 1) layer (28) on the Gan buffer layer (26). An AlxGa1-xN (0≤x≤0.5) barrier layer (30) is on the AlyGa1-yN layer (28), opposite the GaN buffer layer (26), the AlyGa1-yN layer (28) having a higher Al concentration than that of the AlxGa1-xN barrirer layer (30). A preferred AlyGa1-yN layer (28) has y=1 or y≃1 and a preferred AlxGa1-xN barrier layer (30) has 0≤0.5. A 2DEG (38) forms at the interface between the GaN buffer layer (26) and the AlyGa1-yN layer (28). Respective source, drain and gate contacts (32, 34, 36) are formed on the AlxGa1-xN barrier layer (30). The HEMT (10) can also include a substrate (22) adjacent to the buffer layer (26), opposite the AlyGa1-yN layer (28) and a nucleation layer (24) can be included between the GaN buffer layer (26) and the substrate (22).

Nanowires, nanostructures and devices fabricated therefrom

Abstract: One-dimensional nanostructures having uniform diameters of less than approximately 200 nm. These inventive nanostructures, which we refer to as “nanowires”, include single-crystalline homostructures as well as heterostructures of at least two single-crystalline materials having different chemical compositions. Because single-crystalline materials are used to form the heterostructure, the resultant heterostructure will be single-crystalline as well. The nanowire heterostructures are generally based on a semiconducting wire wherein the doping and composition are controlled in either the longitudinal or radial directions, or in both directions, to yield a wire that comprises different materials. Examples of resulting nanowire heterostructures include a longitudinal heterostructure nanowire (LOHN) and a coaxial heterostructure nanowire (COHN).

Conceptual integration and metaphor: An event-related potential study

Abstract: Event-related brain potentials (ERPs) were recorded from 18 normal adults as they read sentences that ended with words used literally, metaphorically, or in an intermediateliteral mapping condition. In the latter condition, the literal sense of the word was used in a way that prompted readers to map conceptual structure from a different domain. ERPs measured from 300 to 500 msec after the onset of the sentence-final words differed as a function of metaphoricity: Literal endings elicited the smallest N400, metaphors the largest N400, whereas literal mappings elicited an N400 of intermediate amplitude. Metaphoric endings also elicited a larger posterior positivity than did either literal or literal mapping words. Consistent with conceptual blending theory, the results suggest that the demands of conceptual integration affect the difficulty of both literal and metaphorical language.

Minimally invasive glaucoma surgical instrument and method

Abstract: Apparatuses and methods for the treatment of glaucoma are provided. The instrument uses either cauterization, a laser to ablate, sonic or ultrasonic energy to emulsify, or mechanical cutting of a portion of the trabecular meshwork. The instrument may also be provided with irrigation, aspiration, and a footplate. The footplate is used to enter Schlemm's canal, serves as a guide, and also protects Schlemm's canal.

A Block-Cipher Mode of Operation for Parallelizable Message Authentication

Abstract: We define and analyze a simple and fully parallelizable blockcipher mode of operation for message authentication. Parallelizability does not come at the expense of serial efficiency: in a conventional, serial environment, the algorithm's speed is within a few percent of the (inherently sequential) CBC MAC. The new mode, PMAC, is deterministic, resembles a standard mode of operation (and not a Carter-Wegman MAC), works for strings of any bit length, employs a single block-cipher key, and uses just max{1, ?|M|/n?} block-cipher calls to MAC a string M ? {0, 1}* using an n-bit block cipher. We prove PMAC secure, quantifying an adversary's forgery probability in terms of the quality of the block cipher as a pseudorandom permutation.

Food Security and Nutritional Outcomes of Preschool-Age Mexican-American Children

Abstract: Objective To examine the relationship of food insecurity to nutrition of Mexican-American preschoolers. Design Cross-sectional survey of low-income Mexican-American families with children of preschool age (3 to 6 years). Data included food security using the Radimer/ Cornell scale; acculturation; parental education; monthly income; past experience of food insecurity; and child weight, height, and frequency of consuming 57 foods. Weight-for-height z scores (WHZ), height- for-age z (HAZ) scores, and the percentage of overweight (≥85th percentile WHZ) were calculated. Subjects/Setting A convenience sample of Mexican-American families (n=211) was recruited through Head Start, Healthy Start, Migrant Education, and the Special Supplemental Nutrition Program for Women, Infants, and Children in Tulare, Fresno, Monterey, and Kern counties in California. Statistical analyses Analysis of variance, t tests, Spearman's correlations, and Mantel Haenszel χ 2 . Results Limited education, lack of English proficiency, and low income were negatively correlated with food security (r=−0.31 to −0.44, P P Applications/Conclusions Dietetics professionals working with low-income Hispanic-American families should screen for different levels of food insecurity to determine needs for nutrition education and other services. J Am Diet Assoc. 2002; 102:924-929 .

SAVE: source address validity enforcement protocol

Abstract: Forcing all IP packets to carry correct source addresses can greatly help network security, attack tracing, and network problem debugging. However, due to asymmetries in today's Internet routing, routers do not have readily available information to verify the correctness of the source address for each incoming packet. In this paper we describe a new protocol, named SAVE, that can provide routers with the information needed for source address validation. SAVE messages propagate valid source address information from the source location to all destinations, allowing each router along the way to build an incoming table that associates each incoming interface of the router with a set of valid source address blocks. This paper presents the protocol design and evaluates its correctness and performance by simulation experiments. The paper also discusses the issues of protocol security, the effectiveness of partial SAVE deployment, and the handling of unconventional forms of network routing, such as mobile IP and tunneling.

Dynamic Replica Placement for Scalable Content Delivery

Abstract: In this paper, we propose the dissemination tree, a dynamic content distribution system built on top of a peer-to-peer location service. We present a replica placement protocol that builds the tree while meeting QoS and server capacity constraints. The number of replicas as well as the delay and bandwidth consumption for update propagation are significantly reduced. Simulation results show that the dissemination tree has close to the optimal number of replicas, good load distribution, small delay and bandwidth penalties for update multicast compared with the ideal case: static replica placement on IP multicast.

Lateralization in motor facilitation during action observation: a TMS study.

Abstract: Action observation facilitates corticospinal excitability. This is presumably due to a premotor neural system that is active when we perform actions and when we observe actions performed by others. It has been speculated that this neural system is a precursor of neural systems subserving language. If this theory is true, we may expect hemispheric differences in the motor facilitation produced by action observation, with the language dominant left hemisphere showing stronger facilitation than the right hemisphere. Furthermore, it has been suggested that body parts are recognized via cortical regions controlling sensory and motor processing associated with that body part. If this is true, then corticospinal facilitation during action observation should be modulated by the laterality of the observed body part. The present study addressed these two issues using TMS for each motor cortex separately as participants observed actions being performed by a left hand, a right hand, or a control stimulus on the computer screen. We found no overall difference between the right and left hemisphere for motor-evoked potential (MEP) size during action observation. However, when TMS was applied to the left motor cortex, MEPs were larger while observing right hand actions. Likewise, when TMS was applied to the right motor cortex, MEPs were larger while observing left hand actions. Our data do not suggest left hemisphere superiority in the facilitating effects of action observation on the motor system. However, they do support the notion of a sensory-motor loop according to which sensory stimulus properties (for example, the image of a left hand or a right hand) directly affect motor cortex activity, even when no motor output is required. The pattern of this effect is congruent with the pattern of motor representation in each hemisphere.

User Interaction Design for Secure Systems

Abstract: The security of any system that is configured or operated by human beings depends on the information conveyed by the user interface, the decisions of the users, and the interpretation of their actions. This paper establishes some starting points for reasoning about security from a user-centred perspective: it proposes to model systems in terms of actors and actions, and introduces the concept of the subjective actor-ability state. Ten principles for secure interaction design are identified; examples of real-world problems illustrate and justify the principles.

Overview of GridRPC: A Remote Procedure Call API for Grid Computing

Abstract: This paper discusses preliminary work on standardizing and implementing a remote procedure call (RPC) mechanism for grid computing. The GridRPC API is designed to address the lack of a standardized, portable, and simple programming interface. Our initial work on GridRPC shows that client access to existing grid computing systems such as NetSolve and Ninf can be unified via a common API, a task that has proven to be problematic in the past.

Best Choices for Regularization Parameters in Learning Theory: On the Bias-Variance Problem

Abstract: whereA is an differential operator and L2 is the Hilbert space of square integrable functions on X with measure ρX on X defined via ρ. This minimization is well-conditioned and solved by straightforward finite dimensional least squares linear algebra to yield fγ,z : X → Y . The problem is posed: How good an approximation is fγ,z to fρ, or measure the error ∫ X(fγ,z − fρ)? and What is the best choice of γ to minimize this error? Our goal in this talk is to give some answers to these questions.

An accessory sec locus of Streptococcus gordonii is required for export of the surface protein GspB and for normal levels of binding to human platelets

Abstract: The translocation of proteins across the bacterial cell membrane is carried out by highly conserved components of the Sec system. Most bacterial species have a single copy of the genes encoding SecA and SecY, which are essential for viability. However, Streptococcus gordonii strain M99 encodes SecA and SecY homologues that are not required for viability or for the translocation of most exported proteins. The genes (secA2 and secY2) reside in a region of the chromosome required for the export of GspB, a 286 kDa cell wall-anchored protein. Loss of GspB surface expression is associated with a significant reduction in the binding of M99 to human platelets, suggesting that it may be an adhesin. Genetic analyses indicate that M99 has a second, canonical SecA homologue that is essential for viability. At least two other Gram-positive species, Streptococcus pneumoniae and Staphylococcus aureus, encode two sets of SecA and SecY homologues. One set is more similar to SecA and SecY of Escherichia coli, whereas the other set is more similar to SecA2 and SecY2 of strain M99. The conserved organization of genes in the secY2-secA2 loci suggests that, in each of these Gram-positive species, SecA2 and SecY2 may constitute a specialized system for the transport of a very large serine-rich repeat protein.

Catheter based balloon for therapy modification and positioning of tissue

Abstract: An apparatus and method for shielding non-target tissues and organs during thermotherapy, brachytherapy or other treatment of a diseased target tissue. The apparatus includes a catheter shaft having input and output lumens and at least one inflatable balloon. A plurality of input lumens within the catheter shaft allows the passage of liquid or gas through an input port and into the interior of the balloon thereby inflating the balloon. The gas or liquid can then be cycled through the inflated balloon through an output port and output lumen and out of the catheter shaft. Temperature sensors or other sensors may be attached to the balloon or catheter to monitor temperature or other conditions at the treatment site. The catheter is positioned between the target tissue or organ and sensitive non-target tissues in proximity to the target tissue and inflated causing a physical separation of tissues as well as a physical shield.

A study of the flow-field evolution and mixing in a planar turbulent jet using direct numerical simulation

Abstract: Turbulent plane jets are prototypical free shear flows of practical interest in propulsion, combustion and environmental flows. While considerable experimental research has been performed on planar jets, very few computational studies exist. To the authors' knowledge, this is the first computational study of spatially evolving three-dimensional planar turbulent jets utilizing direct numerical simulation. Jet growth rates as well as the mean velocity, mean scalar and Reynolds stress profiles compare well with experimental data. Coherency spectra, vorticity visualization and autospectra are obtained to identify inferred structures. The development of the initial shear layer instability, as well as the evolution into the jet column mode downstream is captured well.The large- and small-scale anisotropies in the jet are discussed in detail. It is shown that, while the large scales in the flow field adjust slowly to variations in the local mean velocity gradients, the small scales adjust rapidly. Near the centreline of the jet, the small scales of turbulence are more isotropic. The mixing process is studied through analysis of the probability density functions of a passive scalar. Immediately after the rollup of vortical structures in the shear layers, the mixing process is dominated by large-scale engulfing of fluid. However, small-scale mixing dominates further downstream in the turbulent core of the self-similar region of the jet and a change from non-marching to marching PDFs is observed. Near the jet edges, the effects of large-scale engulfing of coflow fluid continue to influence the PDFs and non-marching type behaviour is observed.

Salinity in the Soil Environment

Abstract: The purpose of this chapter is to provide plant scientists with a background on the nature of soil salinity with a particular emphasis on irrigated agriculture. Since the chemistry of soil solutions plays a major role in soil salinity, considerable details on this topic are offered. Chemical speciation in the soil solution should be of importance to plant scientists. The dynamic nature of soil salinity in the rootzone affects performance of plants. Profile distribution of salts is affected by leaching fraction and changes with changing water content from irrigation and rootwater extraction. Soluble salts in soils are highly mobile and transported by water through mass flow and dispersion. Irrigation water management is one of the keys in maintaining salt balance in the rootzone. Growing regulations on the disposal and management of poor quality drainage waters is now exacerbating the maintenance of salt balance in the rootzone in irrigated lands.