Nonideality-Aware Training for Accurate and Robust Low-Power Memristive Neural Networks

Recent years have seen a rapid rise of artificial neural networks being employed in a number of cognitive tasks. The ever-increasing computing requirements of these structures have contributed to a desire for novel technologies and paradigms, including memristor-based hardware accelerators. Solutions based on memristive crossbars and analog data processing promise to improve the overall energy efficiency. However, memristor nonidealities can lead to the degradation of neural network accuracy, while the attempts to mitigate these negative effects often introduce design trade-offs, such as those between power and reliability. In this work, authors design nonideality-aware training of memristor-based neural networks capable of dealing with the most common device nonidealities. The feasibility of using high-resistance devices that exhibit high I-V nonlinearity is demonstrated-by analyzing experimental data and employing nonideality-aware training, it is estimated that the energy efficiency of memristive vector-matrix multipliers is improved by almost three orders of magnitude (0.715 TOPs^-1 W^-1 to 381 TOPs^-1 W^-1 ) while maintaining similar accuracy. It is shown that associating the parameters of neural networks with individual memristors allows to bias these devices toward less conductive states through regularization of the corresponding optimization problem, while modifying the validation procedure leads to more reliable estimates of performance. The authors demonstrate the universality and robustness of this approach when dealing with a wide range of nonidealities.

Neuromorphic Dynamics at the Nanoscale in Silicon Suboxide RRAM

Resistive random-access memories, also known as memristors, whose resistance can be modulated by the electrically driven formation and disruption of conductive filaments within an insulator, are promising candidates for neuromorphic applications due to their scalability, low-power operation and diverse functional behaviors. However, understanding the dynamics of individual filaments, and the surrounding material, is challenging, owing to the typically very large cross-sectional areas of test devices relative to the nanometer scale of individual filaments. In the present work, conductive atomic force microscopy is used to study the evolution of conductivity at the nanoscale in a fully CMOS-compatible silicon suboxide thin film. Distinct filamentary plasticity and background conductivity enhancement are reported, suggesting that device behavior might be best described by composite core (filament) and shell (background conductivity) dynamics. Furthermore, constant current measurements demonstrate an interplay between filament formation and rupture, resulting in current-controlled voltage spiking in nanoscale regions, with an estimated optimal energy consumption of 25 attojoules per spike. This is very promising for extremely low-power neuromorphic computation and suggests that the dynamic behavior observed in larger devices should persist and improve as dimensions are scaled down.

Memristor-Based Edge Detection for Spike Encoded Pixels

Memristors have many uses in machine learning and neuromorphic hardware. From memory elements in dot product engines to replicating both synapse and neuron wall behaviors, the memristor has proved a versatile component. Here we demonstrate an analog mode of operation observed in our silicon oxide memristors and apply this to the problem of edge detection. We demonstrate how a potential divider exploiting this analog behavior can prove a scalable solution to edge detection. We confirm its behavior experimentally and simulate its performance on a standard testbench. We show good performance comparable to existing memristor based work with a benchmark score of 0.465 on the BSDS500 dataset, while simultaneously maintaining a lower component count.

Simulation of Inference Accuracy Using Realistic RRAM Devices

Resistive Random Access Memory (RRAM) is a promising technology for power efficient hardware in applications of artificial intelligence (AI) and machine learning (ML) implemented in non-von Neumann architectures. However, there is an unanswered question if the device non-idealities preclude the use of RRAM devices in this potentially disruptive technology. Here we investigate the question for the case of inference. Using experimental results from silicon oxide (SiO_x) RRAM devices, that we use as proxies for physical weights, we demonstrate that acceptable accuracies in classification of handwritten digits (MNIST data set) can be achieved using non-ideal devices. We find that, for this test, the ratio of the high- and low-resistance device states is a crucial determinant of classification accuracy, with ~96.8% accuracy achievable for ratios >3, compared to ~97.3% accuracy achieved with ideal weights. Further, we investigate the effects of a finite number of discrete resistance states, sub-100% device yield, devices stuck at one of the resistance states, current/voltage non-linearities, programming non-linearities and device-to-device variability. Detailed analysis of the effects of the non-idealities will better inform the need for the optimization of particular device properties.

Sensing and Discrimination of Explosives at Variable Concentrations with a Large-Pore MOF as Part of a Luminescent Array

Metal-organic frameworks (MOFs) have shown great promise for sensing of dangerous chemicals, including environmental toxins, nerve agents, and explosives. However, challenges remain, such as the sensing of larger analytes and the discrimination between similar analytes at different concentrations. Herein, we present the synthesis and development of a new, large-pore MOF for explosives sensing and demonstrate its excellent sensitivity against a range of relevant explosive compounds including trinitrotoluene and pentaerythritol tetranitrate. We have developed an improved, thorough methodology to eliminate common sources of error in our sensing protocol. We then combine this new MOF with two others as part of a three-MOF array for luminescent sensing and discrimination of five explosives. This sensor works at part-per-million concentrations and, importantly, can discriminate explosives with high accuracy without reference to their concentration.

The interplay between structure and function in redox-based resistance switching

We report a study of the relationship between oxide microstructure at the scale of tens of nanometres and resistance switching behaviour in silicon oxide.

Silicon Oxide (SiOx ): A Promising Material for Resistance Switching?

Interest in resistance switching is currently growing apace. The promise of novel high-density, low-power, high-speed nonvolatile memory devices is appealing enough, but beyond that there are exciting future possibilities for applications in hardware acceleration for machine learning and artificial intelligence, and for neuromorphic computing. A very wide range of material systems exhibit resistance switching, a number of which-primarily transition metal oxides-are currently being investigated as complementary metal-oxide-semiconductor (CMOS)-compatible technologies. Here, the case is made for silicon oxide, perhaps the most CMOS-compatible dielectric, yet one that has had comparatively little attention as a resistance-switching material. Herein, a taxonomy of switching mechanisms in silicon oxide is presented, and the current state of the art in modeling, understanding fundamental switching mechanisms, and exciting device applications is summarized. In conclusion, silicon oxide is an excellent choice for resistance-switching technologies, offering a number of compelling advantages over competing material systems.

Spike-Timing Dependent Plasticity in Unipolar Silicon Oxide RRAM Devices

Resistance switching, or Resistive RAM (RRAM) devices show considerable potential for application in hardware spiking neural networks (neuro-inspired computing) by mimicking some of the behavior of biological synapses, and hence enabling non-von Neumann computer architectures. Spike-timing dependent plasticity (STDP) is one such behavior, and one example of several classes of plasticity that are being examined with the aim of finding suitable algorithms for application in many computing tasks such as coincidence detection, classification and image recognition. In previous work we have demonstrated that the neuromorphic capabilities of silicon-rich silicon oxide (SiO_x) resistance switching devices extend beyond plasticity to include thresholding, spiking, and integration. We previously demonstrated such behaviors in devices operated in the unipolar mode, opening up the question of whether we could add plasticity to the list of features exhibited by our devices. Here we demonstrate clear STDP in unipolar devices. Significantly, we show that the response of our devices is broadly similar to that of biological synapses. This work further reinforces the potential of simple two-terminal RRAM devices to mimic neuronal functionality in hardware spiking neural networks.

Nanoscale Transformations in Metastable, Amorphous, Silicon-Rich Silica

Electrically biasing thin films of amorphous, substoichiometric silicon oxide drives surprisingly large structural changes, apparent as density variations, oxygen movement, and ultimately, emission of superoxide ions. Results from this fundamental study are directly relevant to materials that are increasingly used in a range of technologies, and demonstrate a surprising level of field-driven local reordering of a random oxide network.

Canine Mastocytoma

Utilizing a modified capillary tube technique, analysis revealed a significantly higher mean blood coagulation time in a group of 14 dogs with mastocytoma when compared to the mean coagulation time of 70 non-mastocytoma dogs. In dogs with mastocytoma, approximately one third had intermediate size tumors and a prolonged mean coagulation time and two thirds had a mean coagulation time that did not differ significantly from the mean of the non-mastocytoma dogs. Evidence for heparin release and possible heparin inactivating mechanisms is reviewed.

X-ray spectromicroscopy investigation of soft and hard breakdown in RRAM devices

Resistive random access memory (RRAM) is considered an attractive candidate for next generation memory devices due to its competitive scalability, low-power operation and high switching speed. The technology however, still faces several challenges that overall prohibit its industrial translation, such as low yields, large switching variability and ultimately hard breakdown due to long-term operation or high-voltage biasing. The latter issue is of particular interest, because it ultimately leads to device failure. In this work, we have investigated the physicochemical changes that occur within RRAM devices as a consequence of soft and hard breakdown by combining full-field transmission x-ray microscopy with soft x-ray spectroscopic analysis performed on lamella samples. The high lateral resolution of this technique (down to 25 nm) allows the investigation of localized nanometric areas underneath permanent damage of the metal top electrode. Results show that devices after hard breakdown present discontinuity in the active layer, Pt inclusions and the formation of crystalline phases such as rutile, which indicates that the temperature increased locally up to 1000 K.

Emulating the Electrical Activity of the Neuron Using a Silicon Oxide RRAM Cell

In recent years, formidable effort has been devoted to exploring the potential of Resistive RAM (RRAM) devices to model key features of biological synapses. This is done to strengthen the link between neuro-computing architectures and neuroscience, bearing in mind the extremely low power consumption and immense parallelism of biological systems. Here we demonstrate the feasibility of using the RRAM cell to go further and to model aspects of the electrical activity of the neuron. We focus on the specific operational procedures required for the generation of controlled voltage transients, which resemble spike-like responses. Further, we demonstrate that RRAM devices are capable of integrating input current pulses over time to produce thresholded voltage transients. We show that the frequency of the output transients can be controlled by the input signal, and we relate recent models of the redox-based nanoionic resistive memory cell to two common neuronal models, the Hodgkin-Huxley (HH) conductance model and the leaky integrate-and-fire model. We employ a simplified circuit model to phenomenologically describe voltage transient generation.

Flexible and fluorophore-doped luminescent solar concentrators based on polydimethylsiloxane

We demonstrate a simple and inexpensive method to fabricate flexible and fluorophore-doped luminescent solar concentrators (LSCs). Polydimethylsiloxane (PDMS) serves as a host material which additionally offers the potential to cast LSCs in arbitrary shapes. The laser dye Pyrromethene 567 is used as a prototype fluorophore, and it is shown that it has a high quantum yield of 93% over the concentration range investigated. The optical efficiency and loss channels of the flexible LSCs are investigated; it is also demonstrated that the efficiency remains high while bending the LSC which is essential for flexible LSCs to make an impact on solar energy.

Conductance tomography of conductive filaments in intrinsic silicon-rich silica RRAM

We present results from an imaging study of filamentary conduction in silicon suboxide resistive RAM devices. We used a conductive atomic force microscope to etch through devices while measuring current, allowing us to produce tomograms of conductive filaments. To our knowledge this is the first report of such measurements in an intrinsic resistance switching material.

Efficiency and loss mechanisms of plasmonic Luminescent Solar Concentrators

Using a hybrid nanoscale/macroscale model, we simulate the efficiency of a luminescent solar concentrator (LSC) which employs silver nanoparticles to enhance the dye absorption and scatter the incoming light. We show that the normalized optical efficiency can be increased from 10.4% for a single dye LSC to 32.6% for a plasmonic LSC with silver spheres immersed inside a thin dye layer. Most of the efficiency enhancement is due to scattering of the particles and not due to dye absorption/re-emission.

Electrically tailored resistance switching in silicon oxide

Resistive switching in a metal-free silicon-based material offers a compelling alternative to existing metal oxide-based resistive RAM (ReRAM) devices, both in terms of ease of fabrication and of enhanced device performance. We report a study of resistive switching in devices consisting of non-stoichiometric silicon-rich silicon dioxide thin films. Our devices exhibit multi-level switching and analogue modulation of resistance as well as standard two-level switching. We demonstrate different operational modes that make it possible to dynamically adjust device properties, in particular two highly desirable properties: nonlinearity and self-rectification. This can potentially enable high levels of device integration in passive crossbar arrays without causing the problem of leakage currents in common line semi-selected devices. Aspects of conduction and switching mechanisms are discussed, and scanning tunnelling microscopy (STM) measurements provide a more detailed insight into both the location and the dimensions of the conductive filaments.

Structural factors impacting carrier transport and electroluminescence from Si nanocluster-sensitized Er ions

We present an analysis of factors influencing carrier transport and electroluminescence (EL) at 1.5 µm from erbium-doped silicon-rich silica (SiOx) layers. The effects of both the active layer thickness and the Si-excess content on the electrical excitation of erbium are studied. We demonstrate that when the thickness is decreased from a few hundred to tens of nanometers the conductivity is greatly enhanced. Carrier transport is well described in all cases by a Poole-Frenkel mechanism, while the thickness-dependent current density suggests an evolution of both density and distribution of trapping states induced by Si nanoinclusions. We ascribe this observation to stress-induced effects prevailing in thin films, which inhibit the agglomeration of Si atoms, resulting in a high density of sub-nm Si inclusions that induce traps much shallower than those generated by Si nanoclusters (Si-ncs) formed in thicker films. There is no direct correlation between high conductivity and optimized EL intensity at 1.5 µm. Our results suggest that the main excitation mechanism governing the EL signal is impact excitation, which gradually becomes more efficient as film thickness increases, thanks to the increased segregation of Si-ncs, which in turn allows more efficient injection of hot electrons into the oxide matrix. Optimization of the EL signal is thus found to be a compromise between conductivity and both number and degree of segregation of Si-ncs, all of which are governed by a combination of excess Si content and sample thickness. This material study has strong implications for many electrically-driven devices using Si-ncs or Si-excess mediated EL.

Electrically pumped silicon waveguide light sources

We report simulations of electrically pumped waveguide emitters in which the emissive layer contains silicon nanoclusters and erbium ions. Plasmonic coupling to metallic or semi-metallic overlayers provides enhancement of the radiative rate of erbium ions, enabling high quantum efficiency emission. Using 2D and 3D finite difference time domain (FDTD) simulations we show that up to 75% of the light emitted from the active layer can be coupled into a nanowire silicon rib waveguide. Our results suggest that such devices, which can readily be fabricated using CMOS processing techniques, pave the way for viable waveguide optical sources to be realized in silicon photonics.

THE CHARACTERIZATION OF STAPHYLOCOCCAL TOXINS : II. THE ISOLATION AND CHARACTERIZATION OF A HOMOGENEOUS STAPHYLOCOCCAL PROTEIN POSSESSING ALPHA HEMOLYTIC, DERMONECROTIC, LETHAL, AND LEUCOCIDAL ACTIVITIES

The continuous flow paper electrophoretic methods used to isolate alpha hemolysin are presented. The purity of the alpha hemolysin preparation is demonstrated by double agar diffusion, immunoelectrophoretic, and ultracentrifugation techniques. Indirect evidence of purity is provided by the fact that rabbit immunized with purified alpha hemolysin produced detectable antibody only to alpha hemolysin. Direct support is given to the "unitarian theory" by the demonstration that purified alpha hemolysin also possessed dermonecrotic, lethal, and leucocidal activities. Further studies dependent on the availability of purified alpha hemolysin are outlined.

Towards population inversion of electrically pumped Er ions sensitized by Si nanoclusters

This study reports the estimation of the inverted Er fraction in a system of Er doped silicon oxide sensitized by Si nanoclusters, made by magnetron sputtering. Electroluminescence was obtained from the sensitized erbium, with a power efficiency of 10(-2)%. By estimating the density of Er ions that are in the first excited state, we find that up to 20% of the total Er concentration is inverted in the best device, which is one order of magnitude higher than that achieved by optical pumping of similar materials.

Modification of the Er3+ radiative lifetime from proximity to silicon nanoclusters in silicon-rich silicon oxide

The lifetime of Er3+ in silicon-rich silicon oxide has been reported with quite widely varying values ranging from 9 ms to 2 ms. In this work, we consider the direct impact of silicon nanoclusters on the erbium radiative lifetime, and show that it is a function of the silicon nanocluster size, and also the erbium proximity to the nanocluster.

Increasing the efficiency of erbium-based sources using silicon quantum dots

Silicon nanoclusters exhibit novel and interesting optical and electrical properties that are not observed in bulk silicon. Moreover, it has been discovered that there exists a strong coupling between nanoclusters and rare-earth ions that results in efficient energy exchange between the two species. This paper presents a review of recent work at University College London in this area, in which we have studied the optical properties of silicon nanoclusters in silica with rare-earth co-dopants and have developed a model for the excitation of erbium ions in erbium-doped silicon nanocrystals via coupling from optically generated excitons confined within the silicon nanoclusters. The model provides a phenomenological description of the exchange mechanism and allows us to evaluate an effective absorption cross-section for erbium that is up to four orders of magnitude higher than the corresponding value in stoichiometric silica. This paper also discusses the origin of the 1.6 eV emission band associated with the silicon nanoclusters and determines absorption cross-sections and excitonic lifetimes for nanoclusters in silica.

Comparison of antipseudomonad activity of chlorine dioxide/chlorous acid-containing gel with commercially available antiseptics

A chlorine dioxide-containing gel was compared with 3 commercially available antimicrobials and 1 antibiotic intended for topical use. This gel was tested at 0.5 X and 4 X and was found to be more effective as a 4 X gel in treating Pseudomonas aeruginosa-infected excised wounds on mice. To further compare this gel with other antiseptics, a murine bioassay was developed. This wound model consisted of an excised cutaneous wound on the dorsum of mice which were irradiated (800 rad) and inoculated with P aeruginosa at 10-fold dilutions, from 10(-2) to 10(-10). The wounds were observed for latency of infection or mice survival time as a function of concentration of viable organisms remaining after treatment. The advantage of this model was demonstrated where a standard curve based on latency did not consume as many test subjects and yet provided an estimate of viable organisms in each wound. In this model, the chlorine dioxide-containing gel was more active than were preparations of providone-iodine, chlorhexidene, or silver sulfadiazine and was similar to polymyxin-bacitracin-neomycin ointment as a topical antiseptic. The effectiveness of the tested gel was reduced if delays in treatment were longer than 1 hour.

Controlled wound repair in guinea pigs, using antimicrobials that alter fibroplasia

The repair processes of incised wounds depend, in part, on fibroplasia induced by soluble mediators from monocytic macrophages. Two topical antimicrobials were evaluated, each of which effectively controlled wound sepsis and yet each had widely different effects on fibroplasia and wound strength. Paired-incision dermal wounds on the flanks of guinea pigs were treated with a substance containing reactive chlorine (Alcide) or with a compound that is a mixture of two surfactants. One side of each guinea pig was treated with one of the antimicrobials (treated wounds); the opposite side was treated with isotonic saline solution (control wounds). At 7, 10, and 16 days after surgery, tensiometric measurements of C31G (a surfactant)-treated wounds were 99%, 139%, and 195% of control wound values, respectively. Alcide-treated wounds were 76%, 58%, and 88% of control wounds, respectively. Wounds treated with chlorhexidine had reduced strength at 7 days (73%) and at 10 days (78%), but by 14 days, they were similar to control wounds (94%). The main difference between the wounds was the amount of collagen formation. Alcide-treated wounds incorporated less than 50% of the amount of 14C-proline than did the wounds treated with C31G. However, Alcide-treated wounds epithelialized as rapidly as did control wounds, and had minimal scar formation. Microscopic evaluations indicated greatly reduced inflammatory infiltrates in Alcide-treated wounds, indicating that reduced wound strength may be associated with lack of fibroblast-stimulating activity by monocytes.

Comparison of early splenic changes associated with replication of viruses in murine monocytic macrophages

An effect of replication of certain viruses in murine monocytic macrophages was manifested by depletion of cells through degenerative and necrotizing changes in thymus-dependent areas of lymphoid structures. In mice infected with murine hepatitis virus (MHV-3) or lactate dehydrogenase virus, these changes were transient in mice killed on postinoculation day (PID) 2. To study these morphologic changes due to viral replication, adult Swiss specific-pathogen-free homozygous nude mice (nu/nu) and their heterozygous haired littermates (nu/+) were inoculated with 10(5) LD50 of MHV-3, euthanatized, and necropsied on PID 1, 2, 4, 6, 8, and 10 along with noninoculated controls. The nu/+ and nu/nu mice killed on PID 2 had lymphocytic karyorrhexis and depletion of cells in the thymus-dependent area. In the heterozygote, these characteristic lesions were transient; whereas in the homozygote, lesions persisted and were present in survivors euthanatized and necropsied on PID 16. Although the intensity of lesions due to MHV-3 varied between nu/+ and nu/nu mice, virus titers determined on liver homogenates were similar for the homozygote and heterozygote during acute disease. Nude and nonnude mice given lactate dehydrogenase virus and killed on PID 2 had a transient depletion of lymphocytes; whereas mice given lymphocytic choriomeningitis virus and killed on PID 4 had a similar lesion. Lesions neither occurred when mice were treated with silica before inoculation, indicating that functional monocytic macrophages were required, nor occurred when another virus, herpes simplex virus type 1, was given.

Histamine-induced suppressor macrophage inhibits fibroblast growth and wound healing

To determine whether there is histamine-induced suppressor activity in macrophage-related functions other than in immunity, extracts and media from a macrophage cell line, RAW 264, were tested for suppressor effect on fibroplasia. The procedure consisted of priming confluent RAW 264 cells in culture with media or cellular extracts of washed mastocytes (P-815). The inoculum was removed from the RAW 264 cells by rinsing with fresh medium 24 hours later, and then with medium replacement and 3 more days of culture. The culture media or extracts of washed RAW 264 cells were tested for suppressor activity. The primed RAW 264 cells were lysed by 4 freeze-thaw cycles and cleared by centrifugation, and the resulting supernatant was tested on fibroblast (3T3) cell growth and wound healing in mice and for suppressor activity on T cells. Replication of 3T3 cells, as quantitated by uptake of [3H]thymidine, was reduced 75% when "suppressor" material from RAW 264 cells was added to 3T3 cultures and not when media or extracts of unprimed RAW 264 cells were added. Tensiometric measurements of wound breaking strength (full-thickness incised wounds) were reduced 31% by day 4 and 47% by postsurgical day 7 when "suppressor" RAW 264 extracts were instilled into wounds. Leukocyte cultures stimulated with phytohemagglutinin had a reduced uptake of [3H]thymidine (suppressed 90% to 95%) when exposed to primed RAW 264 extracts, whereas kidney cell culture lines were unaffected. The data obtained indicated that mastocyte (histamine)-induced suppressor factors are present for fibroblast activity as well as T-cell function.

Mice and rabbit models for oral and percutaneous absorption and disposition of amphoteric surfactant C31G

A topical antimicrobial agent (C31G), composed of amphoteric surfactants (alkyl betaines and alkyl amine oxides), had a significant (P less than 0.001) and concentration dependent rate of percutaneous absorption in mice and rabbits. Percutaneous absorption studies (3 concentrations for 3 exposure periods) in mice indicated that dermal interaction resulted in nonlinear changes for rate of penetration and transport as a function of exposure and concentration. Kinetic studies of absorption and disposition after oral dosing in mice with [3H]C31G were used to determine the body burden (0.21 g/kg of body weight) at a no effect level. Dermal penetration (P) and transport (T) resulting from percutaneous exposure at variations of time and dosage concentrations were shown to fit the equation T = a + k ln t. The regression coefficient k represents the characteristic change of T with exposure time (t). For low concentrations k equaled 1.89 and at the high concentration k equaled 2.68. This increase of T indicated the interaction of the agent with the dermal barrier at high concentrations. Dermal transport in the rabbit was less than one-fourth of that in the mouse. Excretion of C31G after oral or dermal dosing was predominantly renal at higher dosage levels, whereas fecal excretion dominated at the lowest dosage levels. The half-life of [3H]C31G in the mouse was 68 hours and 86 hours in the rabbit. Data and statistical methods allowed prediction of the effects of daily exposures

Characterization of deoxyribonucleic acid from cells infected with Aleutian disease virus

Viral DNA was extracted from Crandell feline kidney (CRFK) cells infected with Aleutian disease virus (ADV) and labeled with [ 3H ]thymidine. The sedimentation coefficient in alkaline sucrose gradients was 16S corresponding to a molecular weight of 1.5 X 10(6). The buoyant densities of DNA from infected and control cells were determined by isopyknic sedimentation in CsCl and NaI gradients. Two additional peaks of [ 3H ]DNA were found in infected cells, but not in control cell extracts. Fractionation of this DNA on hydroxylapatite indicated that the new peaks represented a single-stranded component, density 1.728 g/cm3, and a double-stranded component, presumed to be a viral replicative intermediate, density 1.718 g/cm3. The target antigen formation in CRFK cells was measured by gamma-irradiation of ADV and assayed for focus formation. The calculated size of ADV based on these measurements was 1.1 X 10(6). The H-1 parvovirus also was shown to have a size of 1.5 X 10(6) daltons for both antigen and plaque formation. The data indicated similarities existed between ADV and other autonomously replicating parvoviruses in most properties, except that less-than-unit length genome of ADV may be transcribed.

Effect of C31G, an antimicrobial surfactant, on healing of incised guinea pig wounds

An anti-infective surfactant composition (C31G) promoted healing of infected and noninfected wounds in guinea pigs. In this animal model, histologic features of wounds treated topically with C31G revealed an increased rate of wound closure associated with decreased inflammatory response and increased C31G fibroblast infiltration and epithelialization. The effect of C31G on fibrin formation, the initial event of wound healing, was compared with effects of anionic and cationic surfactants that delay healing. The surfactants had different effects on clotting time, platelet activation, and cross-linkage of the stabilized clot. Seemingly, C31G increased the protein cross-linking of fibrin in clots containing fibronectin.

Delayed wound healing in mice associated with viral alteration of macrophages

Mice acutely and chronically infected with Sendai virus had impaired healing of incisional wounds. This impairment could be overcome by instilling the macrophage-stimulators zymosan and glucan into full-thickness incised wounds, whereas levamisole, an immunomodulator, had no effect on tensile strength of these wounds (breaking strengths). Another commonly occurring murine virus, murine hepatitis virus, also reduced wound tensile strength in infected mice. However, the murine strain of herpes simplex virus, type 1, which caused greater morbidity, did not reduce tensile strength. Although measurements of wound length and wound breaking strength clearly showed the adverse effect of viral infection, histologic evaluation of wounds did not consistently reveal a similar change in composition of wound "cell aggregation centers" for mice infected with the Sendai and murine hepatitis viruses.

Modulation of early cellular events in wound healing in mice

Wound healing experiments were conducted in random-bred Swiss mice to determine the effect on antimicrobial surfactants and macrophage stimulators on wound measurements, histologic repair, and wound breaking strengths. In selection of mice, Sendai virus antibody-positive mice healed more slowly than did mice with no detectable titer to Sendai virus. Studies were conducted with Sendai virus-free mice that had C31G (an antimicrobial surfactant), alkyl amine oxide, zymosan, glucan, or phosphate-buffered isotonic saline solution instilled into full-thickness incised wounds. The early events in the repair process indicated a greater degree of inflammatory response comprised mainly of polymorphonuclear leukocytes with subsequent large numbers of monocytes in C31G and alkyl amine oxide-treated wounds. Although zymosan did not induce as large a number of monocytes, the degree of fibroplasia was as great as in wounds in which numbers were higher. The effect of zymosan could be blocked by the addition of N-alpha-p-tosyl-L-lysine chloromethyl ketone to wounds. Wound breaking strength 3 days after surgery was greatest for glucan-treated mice (134 +/- 37 g) whereas that in C31G-treated mice (77 +/- 31 g) was less than that of the controls (92 +/- 37 g). By day 7, there was no significant difference in breaking strength between control and glucan-treated wounds; however, C31G-treated wounds remained substantially weaker than control wounds.

Anti-deoxyribonucleic acid antibody associated with persistent infection of mink with Aleutian disease virus

Anti-deoxyribonucleic acid (DNA) antibody was quantitated in sera from mink infected with Aleutian disease virus (ADV). During the course of the disease after experimental infection, the amount of anti-DNA antibody increased 60% initially, but then decreased to an intermediate level when measured 2.5 months later. The percentage of serum immunoglobulin, however, steadily increased over 3.5-fold during this period, resulting in the characteristic gammopathy. Correlation between the level of anti-DNA antibody and hypergammaglobulinemia was demonstrated with sera from chronically infected mink. Competition experiments and use of labeled nucleic acids indicated that the immunoactivity was more specific for double-stranded DNA than single-stranded DNA or ribonucleic acid. Anti-DNA antibody was found in purified immunoglobulin from chronically infected mink. Differences in avidity of antibody to DNA among antisera that had the same equivalence point were found. Avidity of antibody for DNA increased during the course of the disease.

Lymphoproliferative diseases of fowl: characterization of transplantable G-B1 Marek's disease tumor cells in culture

A transplantable Marek's disease tumor, derived and maintained through in vivo passage in syngeneic G-B1 chickens, was established in cell culture and characterized. The cells (GBT cells) grew in suspension and appeared morphologically similar to other Marek's lymphoblastoid lines except for prominent nucleoli in GBT cells. The number of chromosomes increased during in vitro cultivation from near triploid to subtetraploid. Chromosome no. 3 was abnormally short. The GBT cells retained surface B1 histocompatibility antigen of the original tumor as well as Marek's disease tumor-specific surface antigen (MATSA); however, infectious Marek's disease virus was not detected by immunofluorescence, electron microscopy, inoculation into susceptible birds, or assay on susceptible cells in culture. Inoculation of as few as 100 cultured cells into syngeneic G-B1 chickens results in tumor formation at the inoculation site, with eventual death of the recipients.

Protides of the Mustelidae: immunoresponse of mustelids to Aleutian mink disease virus

Members of North American Mustelidae were tested for their response to inoculation with 10(6) infective doses of Aleutian disease virus. In subfamily Mustelinae, 3 species in the genus Mustela (M vision, M erminea, and M putorius) and 2 species in genus Martes (Ma pennanti and Ma americana) responded immunologically with some features resembling Aleutian disease in mink. In subfamily Mephitinae, only Mephitis mephitis responded, and others of the subfamily did not, nor did members of subfamilies Melinae and Lutrinae. The responses observed ranged from development of detectable antibody levels determined by counterimmunoelectrophoresis to histopathologic changes typical of Aleutian disease.

Properties of Aleutian disease virus assayed with feline kidney cells

Properties of Aleutian disease virus (ADV) were studied using feline kidney cells, line CRFK, to assay virus by the induction of nuclear antigen. ADV nuclear antigen was detected by immunofluorescent staining. Titers of virus obtained from mink spleens at 10-8 days after infection were usually between 10(3) and 10(5) infectious units per gram of spleen. ADV was purified by fluorocarbon extraction, differential centrifugation, biogel A-15 chromatography and CsCl equilibrium centrifugation. The molecular weight of the virus was estimated to be 3-5 X 10(5) daltons. The density of antigen-inducing virus in equilibrium CsCl gradients was 1.32--1.34 g/cm3. On velocity sucrose gradients, antigen-inducing virus had a sedimentation coefficient of approximately 110S. The virus was not neutralized by sera from chronically infected mink and ferrets and by sera from experimentally infected mink. ADV was resistant to ionic and nonionic detergents and lipid solvents. The titer of partially purified virus was reduced as much as 700-fold by proteolytic enzymes but not by DNase or RNase. The virus was inactivated slowly at 56 degrees C; the initial half-life was 90 minutes. It is concluded that the properties of ADV can be determined by assay in CRFK cells, thus facilitating virological study of the disease.

Lymphoproliferative diseases of fowl: JM-V leukemic lymphoblasts in cell culture

JM-V leukemic lymphoblasts were established in cell culture. The cultured cells (JM-VLC cells) were transplantable in young chicks and produced a disease indistinguishable from JM-V lymphoblastic leukemia as initiated by whole-blood inoculation. JM-VLC cells maintained a normal female karyotype through 13 passages in Rhode Island Red cockerels. With the use of JM-V antisera and antisera from birds with naturally occurring Marek's disease (MD), specific antigens were detected on the surfaces of living cells. Intracellular antigens were detected with anti-MD virus sera after cultivation for at least 1 day at 37 degrees C. In spite of the expression of MD antigens, the presence of herpesvirus particles associated with the cultured cells, and the occurrence of foci of multinucleated cells in kidney cultures from chicks inoculated with cellfree preparations of JM-VLC cells, the pathologic potential of the cultured cells was that of JM-V leukemia.

Expression of Aleutian mink disease antigen in cell culture

Infection of CRFK feline kidney cells with Aleutian disease vurus leads to production of virus-induced antigen(s) in the nucleus which could be demonstrated by the fluorescent-antibody technique. The number of fluorescent nuclei was lineraly dependent on the dilution of the inoculum, but rarely exceeded 20% of the cells. Aleutian disease nuclear antigen was only transiently detectable. The virus-induced antigen was detected after infection of cells of several divergent species; however, the CRFK line of feline kidney cells was the most susceptible. Inhibitor studies indicated that deoxyribonucleic acid synthesis, ribonucleic acid synthesis, and protein synthesis were required for viral antigen production. Cell growth was also a requirement for synthesis of viral antigen, An in situ radioimmune assay was used to measure binding of 125I-labeled mink anti-Aleutian disease virus to infected cells and competition with unlabeled sera. The system is suitable for quantitation of infectivity.

Lymphoproliferative diseases of fowl: chromosome breaks caused in lymphocytes by JM-V herpesvirus

Chromosome preparations were made of bone marrow cells and peripheral lymphocytes isolated from chicks that developed leukemia following infection with JM-V herpes-virus. Karyotypic analysis revealed a high frequency of chromosome breaks and aneuploidy, as well as some pulverization of chromosomes. The number of chromosome breaks began to increase at 2-3 days post infection, and by 5 days post infection it reached 12.7% of bone marrow cells and 17.2% of peripheral lymphocytes. Similarly, the number of aneuploid metaphase figures increased rapidly and reached 12% of bone marrow cells and 19% of peripheral lymphocytes at 5 days post infection. Some specificity was observed in the chromosomes that were affected.

Mobility of sodium dodecyl sulphate - protein complexes

Reduced and unreduced lysozyme aggregates formed by formaldehyde cross-linking comprise a set of model compounds for studying the effects of protein conformation on the electrophoretic mobilities of sodium dodecyl sulphate-protein complexes. The reduced aggregates were indistinguisable from normal proteins, but the unreduced aggregates migrated anomalously fast by about 14%. Contrary to expectations, plots of logarithm Rf versus Kr (retardation coefficient) failed to reveal an unusual conformation for the unreduced aggregates. Thus the anomalous mobility caused by several intramolecular disulphide bonds escaped detection by the above two diagnostic plots. Also included in this paper is a discussion of the implications of these results with regard to current models for sodium dodecyl sulphate-protein complexes.