Trilogy on Computing Maximal Eigenpair

The eigenpair here means the twins consist of eigenvalue and its eigenvector. This paper introduces the three steps of our study on computing the maximal eigenpair. In the first two steps, we construct efficient initials for a known but dangerous algorithm, first for tridiagonal matrices and then for irreducible matrices, having nonnegative off-diagonal elements. In the third step, we present two global algorithms which are still efficient and work well for a quite large class of matrices, even complex for instance.Comment: Updated versio

Implicit learning: What does it all mean - Response

In the original target article (Shanks & St. John 1994), one of our principal conclusions was that there is almost no evidence that learning can occur outside awareness. The continuing commentaries raise some interesting questions, especially about the definition of learning, but do not lead us to abandon our conclusion

T cell recognition of nonpolymorphic determinants on H-2 class I molecules.

Recognition of polymorphic determinants on class I or class II MHC Ag is required for T lymphocyte responses. Using cell-size artificial membranes (pseudocytes) bearing H-2 class I Ag it is demonstrated that T cells can, in addition, recognize nonpolymorphic determinants on class I proteins. Pseudocytes bearing class I alloantigen stimulate in vitro generation of secondary allogeneic CTL responses. At a suboptimal alloantigen surface density, incorporation of class I molecules identical to those of the responder cells (self-H-2) or from third-party cells resulted in dramatically enhanced responses, whereas incorporation of class II proteins had no effect. The receptor that mediates recognition of conserved class I determinants has not been identified, but results of antibody blocking studies are consistent with the Lyt-2/3 complex of CTL having this role. Thus, class I proteins on Ag-bearing cells can have two distinct roles in T cell activation, one involving recognition of polymorphic determinants by the Ag-specific receptor and the other involving recognition of conserved determinants

Technology strategy and innovation: the use of derivative strategies in the aerospace industry

Strategy has become an increasingly important theme within the management of innovation. This is reflected in the increasing amount of attention given to topics such as technology strategy within the innovation literature. However research into technology strategy has tended to focus on technology acquisition rather than technology exploitation. This paper focuses on one often neglected way in which companies can exploit the technological resources at their disposal, namely through the use of a derivative strategy where new technology is combined with old products or parts of old products in order to develop new products. The paper explores this type of strategy by means of a case study from the commercial jet engine sector of the aerospace industry. The case study provides an opportunity not only to explore the nature of derivative strategies in detail it also highlights the benefits, both direct and indirect, to be gained from this type of strategy as a means of exploiting an organisation's technological resources. The paper shows how a derivative strategy can contribute to the broader strategic goals of companies in technology based industries through strategies designed to ensure the most effective utilisation of the technology base

Hydrogen SI and HCCI Combustion in a Direct-Injection Optical Engine

Hydrogen has been largely proposed as a possible alternative fuel for internal combustion engines. Its wide flammability range allows higher engine efficiency with leaner operation than conventional fuels, for both reduced toxic emissions and no CO2 gases. Independently, Homogenous Charge Compression Ignition (HCCI) also allows higher thermal efficiency and lower fuel consumption with reduced NOX emissions when compared to Spark-Ignition (SI) engine operation. For HCCI combustion, a mixture of air and fuel is supplied to the cylinder and autoignition occurs from compression; engine is operated throttle-less and load is controlled by the quality of the mixture, avoiding the large fluid-dynamic losses in the intake manifold of SI engines. HCCI can be induced and controlled by varying the mixture temperature, either by Exhaust Gas Recirculation (EGR) or intake air pre-heating. A combination of HCCI combustion with hydrogen fuelling has great potential for virtually zero CO2 and NOX emissions. Nevertheless, combustion on such a fast burning fuel with wide flammability limits and high octane number implies many disadvantages, such as control of backfiring and speed of autoignition and there is almost no literature on the subject, particularly in optical engines. Experiments were conducted in a single-cylinder research engine equipped with both Port Fuel Injection (PFI) and Direct Injection (DI) systems running at 1000 RPM. Optical access to in-cylinder phenomena was enabled through an extended piston and optical crown. Combustion images were acquired by a high-speed camera at 1°or 2°crank angle resolution for a series of engine cycles. Spark-ignition tests were initially carried out to benchmark the operation of the engine with hydrogen against gasoline. DI of hydrogen after intake valve closure was found to be preferable in order to overcome problems related to backfiring and air displacement from hydrogens low density. HCCI combustion of hydrogen was initially enabled by means of a pilot port injection of n-heptane preceding the main direct injection of hydrogen, along with intake air preheating. Sole hydrogen fuelling HCCI was finally achieved and made sustainable, even at the low compression ratio of the optical engine by means of closed-valve DI, in synergy with air-pre-heating and negative valve overlap to promote internal EGR. Various operating conditions were analysed, such as fuelling in the range of air excess ratio 1.2-3.0 and intake air temperatures of 200-400°C. Finally, both single and double injections per cycle were compared to identify their effects on combustion development. Copyright © 2009 SAE International

Flame chemiluminescence and OH LIF imaging in a hydrogen-fuelled spark-ignition engine

Research into novel internal combustion engines requires consideration of the diversity in future fuels in an attempt to reduce drastically CO2 emissions from vehicles and promote energy sustainability. Hydrogen has been proposed as a possible fuel for future internal combustion engines. Hydrogen’s wide flammability range allows higher engine efficiency with much leaner operation than conventional fuels, for both reduced toxic emissions and no CO2 gases. This paper presents results from an optical study of combustion in a spark-ignition research engine running with direct injection and port injection of hydrogen. Crank-angle resolved flame chemiluminescence images were acquired and post-processed for a series of consecutive cycles in order to calculate in-cylinder rates of flame growth. Laser induced fluorescence of OH was also applied on an in-cylinder plane below the spark plug to record detailed features of the flame front for a series of engine cycles. The tests were performed at various air-to-fuel ratios, typically in a range of φ = 0.50–0.83 at 1000 RPM with 0.5 bar intake pressure. The engine was also run with gasoline in direct-injection and port-injection modes to compare with the operation on hydrogen. The observed combustion characteristics were analysed with respect to laminar and turbulent burning velocities, as well as flame stretch. An attempt was also made to review relevant hydrogen work from the limited literature on the subject and make comparisons were appropriate

Controlled autoignition of hydrogen in a direct-injection optical engine

Research into novel internal combustion engines requires consideration of the diversity in future fuels in an attempt to reduce drastically CO2 emissions from vehicles and promote energy sustainability. Hydrogen has been proposed as a possible fuel for future internal combustion engines and can be produced from renewable sources. Hydrogen’s wide flammability range allows higher engine efficiency than conventional fuels with both reduced toxic emissions and no CO2 gases. Most previous work on hydrogen engines has focused on spark-ignition operation. The current paper presents results from an optical study of controlled autoignition (or homogeneous charge compression ignition) of hydrogen in an engine of latest spark-ignition pentroof combustion chamber geometry with direct injection of hydrogen (100 bar). This was achieved by a combination of inlet air preheating in the range 200–400 °C and residual gas recirculated internally by negative valve overlap. Hydrogen fuelling was set to various values of equivalence ratio, typically in the range ϕ = 0.40–0.63. Crank-angle resolved flame chemiluminescence images were acquired for a series of consecutive cycles at 1000 RPM in order to calculate in-cylinder rates of flame expansion and motion. Planar Laser Induced Fluorescence (LIF) of OH was also applied to record more detailed features of the autoignition pattern. Single and double (i.e. ‘split’ per cycle) hydrogen injection strategies were employed in order to identify the effect of mixture preparation on autoignition’s timing and spatial development. An attempt was also made to review relevant in-cylinder phenomena from the limited literature on hydrogen-fuelled spark-ignition optical engines and make comparisons were appropriate

Canards and curvature: nonsmooth approximation by pinching

In multiple time-scale (singularly perturbed) dynamical systems, canards are counterintuitive solutions that evolve along both attracting and repelling invariant manifolds. In two dimensions, canards result in periodic oscillations whose amplitude and period grow in a highly nonlinear way: they are slowly varying with respect to a control parameter, except for an exponentially small range of values where they grow extremely rapidly. This sudden growth, called a canard explosion, has been encountered in many applications ranging from chemistry to neuronal dynamics, aerospace engineering and ecology. Canards were initially studied using nonstandard analysis, and later the same results were proved by standard techniques such as matched asymptotics, invariant manifold theory and parameter blow-up. More recently, canard-like behaviour has been linked to surfaces of discontinuity in piecewise-smooth dynamical systems. This paper provides a new perspective on the canard phenomenon by showing that the nonstandard analysis of canard explosions can be recast into the framework of piecewise-smooth dynamical systems. An exponential coordinate scaling is applied to a singularly perturbed system of ordinary differential equations. The scaling acts as a lens that resolves dynamics across all time-scales. The changes of local curvature that are responsible for canard explosions are then analyzed. Regions where different time-scales dominate are separated by hypersurfaces, and these are pinched together to obtain a piecewise-smooth system, in which curvature changes manifest as discontinuity-induced bifurcations. The method is used to classify canards in arbitrary dimensions, and to derive the parameter values over which canards form either small cycles (canards without head) or large cycles (canards with head)

Carbohydrate moieties of major histocompatibility complex class I alloantigens are not required for their recognition by T lymphocytes.

The ability to generate specific cytotoxic responses using purified major histocompatibility complex (MHC) antigen in liposomes has made it possible to directly assess the importance of class I carbohydrate moieties in T cell recognition of alloantigen. Deglycosylation of affinity-purified H-2Kk to yield a single glycan-free product did not alter the specificity, the magnitude, nor the dose range of the cytotoxic T lymphocyte (CTL) response to the class I antigen. It can be concluded that carbohydrate moieties are not required to maintain the necessary conformation of the MHC protein, nor to interact with either the antigen-specific receptor or accessory proteins on precursor CTL