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At least 667 records · Page 37Linked to original sources
PubMed2006

Development and multiplexed control of latching pneumatic valves using microfluidic logical structures.

Novel latching microfluidic valve structures are developed, characterized, and controlled independently using an on-chip pneumatic demultiplexer. These structures are based on pneumatic monolithic membrane valves and depend upon their normally-closed nature. Latching valves consisting of both three- and four-valve circuits are demonstrated. Vacuum or pressure pulses as short as 120 ms are adequate to hold these latching valves open or closed for several minutes. In addition, an on-chip demultiplexer is demonstrated that requires only n pneumatic inputs to control 2(n-1) independent latching valves. These structures can reduce the size, power consumption, and cost of microfluidic analysis devices by decreasing the number of off-chip controllers. Since these valve assemblies can form the standard logic gates familiar in electronic circuit design, they should be useful in developing complex pneumatic circuits.

Journal Article↗
PubMed1994

What changes in health behaviour might nurses logically expect from their health education work?

This paper examines nurses' health education work from a philosophical perspective. Two key concepts, choice and autonomy, are explored by analysing examples of the health education work of the practice nurse and the health visitor. As a result, the question, 'what changes in health behaviour might nurses logically expect from their health education work?' is considered. The individualistic assumption within nurses' health education work, that individual patients and clients face certain choices and are able to exert some control over their health status, is reviewed. Choices related to healthy eating, for example, are recognized to be constrained by issues such as finance, time and social circumstances. The choice not to smoke is similarly constrained, for example, by social deprivation, cultural patterns and advertising. The paper both rejects an overly determined conception of patients and clients where they are viewed as unable to make any choices, but also cautions against the danger of victim-blaming. Constraints on patients' and clients' autonomy in health education by nurses are also considered. These limitations on health education work include, for example, a lack of scientific knowledge related to an individual's propensity to develop disease. In contrast, health education work within nursing may also be seen as enabling people to be more autonomous in relation to their health by imparting knowledge about health risks. Health education work by nurses thus emerges from the analysis as a constrained but valuable activity.

Choice Behavior↗
PubMed1999

Cubital tunnel syndrome: anterior transposition as a logical approach to complete nerve decompression.

In it's native position, deep to Osborne's ligament, within the retrocondylar groove of the elbow, the ulnar nerve courses with a significant lever distance posterior to the elbow axis of rotation. In this position, flexion of the elbow places longitudinal traction and local compression forces on the nerve. This biomechanical consideration, as well as variations in anatomy, may potentially contribute to a decrease in the nerve's microcirculation and partial pressure of oxygen, leading to cubital tunnel syndrome. Anterior transposition of the ulnar nerve at the elbow for cubital tunnel syndrome will eliminate natural as well as pathological traction and compression forces; the procedure relieves the nerve of potential microcirculation compromise. Risks of mobilizing the nerve for transposition, however, include iatrogenic ischemia from segmental separation of the nerve from its mesentery-like extrinsic blood supply. Intrinsic interstitial "step-ladder" vessels within the substance of the ulnar nerve allow it to be separated from its extrinsic circulation safely, making anterior transposition a logical and reasonable choice for cubital tunnel syndrome requiring operative intervention.

Cubital Tunnel Syndrome↗
PubMed2004

A logical (discrete) formulation for the storage and recall of environmental signals in plants.

When subjected to an appropriate asymmetric stimulus, seedlings of Bidens pilosa L. "store" a symmetry-breaking instruction that will finally take effect (in the form of a differential growth of the cotyledonary buds) only if the plants are in a state in which they can "recall" this information. The ability of the plants to recall the stored symmetry-breaking instruction may be switched "on" or "off" by the application of a variety of stimuli. Although its detailed phenomenology is rather complicated, the overall behaviour of the plant storage/recall system can be modelled by use of an asynchronous, logical (discrete) description involving positive and negative feedback circuits, which are required for the existence of multi-stationarity and stability, respectively. The state tables, as used in this formalism, give a concise and easy-to-handle description of the evolution of the system and make it particularly easy to determine its stable states. This modelling approach may be extended to the formulation of many other experimental systems.

Biological Clocks↗
PubMedDate not supplied

There is no gap 'per se' between theory and practice: Research knowledge and clinical knowledge are developed in different contexts and follow their own logic.

The aim of this article is to highlight relations between theory and practice and the genesis of professional action in clinical nursing and among researchers. With use of a sociologically based empirical approach, focus is placed on the knowledge involved in the work of researchers and practitioners in terms of the source of their knowledge. Unlike a dominant barrier paradigm, theory and practice have different logics; they are not on a continuum nor are they hierarchically ordered. They exist in their own right as theoretical knowledge and practical knowledge. In daily practice, clinical nurses are inspired and learn from the context, including each other, and they are active producers of knowledge, not simply recipients of knowledge. This study, therefore, claims that there is no research-practice gap "in itself" (per se) as argued in the "barriers paradigm."

Ethics, Clinical↗
PubMed2005

Electrical addressing of confined quantum systems for quasiclassical computation and finite state logic machines.

Conduction spectroscopy measures the current I through a nanosystem as a function of the voltage V between two electrodes. The differential conductance, dI/dV, has peaks that can be assigned to resonance conditions with different electronic levels of the system. Between these increments, the current has roughly constant plateaus. We discuss how measurements of the current vs. voltage can be used to perform Boolean operations and hence construct finite state logic machines and combinational circuits. The inputs to the device are the source-drain voltage, including its sign, and a gate voltage applied in a manner analogous to optical Stark spectroscopy. As simple examples, we describe a two-state set-reset machine (a machine whose output depends on the input and also on its present state) and a full adder circuit (a circuit that requires three inputs and provides two outputs).

Journal Article↗
PubMed2006

Concatenated logic gates using four coupled biocatalysts operating in series.

The assembly of three concatenated enzyme-based logic gates consisting of OR, AND, XOR is described. Four biocatalysts, acetylcholine esterase, choline oxidase, microperoxidase-11, and the NAD+-dependent glucose dehydrogenase, are used to assemble the gates. Four inputs that include acetylcholine, butyrylcholine, O2, and glucose are used to drive the concatenated-gates system. The cofactor NAD+, and its reduced 1,4-dihydro form, NADH, are used as a reporter couple, and these provide an optical output for the gates. The modulus of the absorbance changes of NADH is used as a readout signal.

Acetylcholinesterase↗
PubMed2003

On schemes of combinatorial transcription logic.

Cells receive a wide variety of cellular and environmental signals, which are often processed combinatorially to generate specific genetic responses. Here we explore theoretically the potentials and limitations of combinatorial signal integration at the level of cis-regulatory transcription control. Our analysis suggests that many complex transcription-control functions of the type encountered in higher eukaryotes are already implementable within the much simpler bacterial transcription system. Using a quantitative model of bacterial transcription and invoking only specific protein-DNA interaction and weak glue-like interaction between regulatory proteins, we show explicit schemes to implement regulatory logic functions of increasing complexity by appropriately selecting the strengths and arranging the relative positions of the relevant protein-binding DNA sequences in the cis-regulatory region. The architectures that emerge are naturally modular and evolvable. Our results suggest that the transcription regulatory apparatus is a "programmable" computing machine, belonging formally to the class of Boltzmann machines. Crucial to our results is the ability to regulate gene expression at a distance. In bacteria, this can be achieved for isolated genes via DNA looping controlled by the dimerization of DNA-bound proteins. However, if adopted extensively in the genome, long-distance interaction can cause unintentional intergenic cross talk, a detrimental side effect difficult to overcome by the known bacterial transcription-regulation systems. This may be a key factor limiting the genome-wide adoption of complex transcription control in bacteria. Implications of our findings for combinatorial transcription control in eukaryotes are discussed.

Bacteria↗
PubMed2024

A conserved molecular logic for neurogenesis to gliogenesis switch in the cerebral cortex.

During development, neural stem cells in the cerebral cortex, also known as radial glial cells (RGCs), generate excitatory neurons, followed by production of cortical macroglia and inhibitory neurons that migrate to the olfactory bulb (OB). Understanding the mechanisms for this lineage switch is fundamental for unraveling how proper numbers of diverse neuronal and glial cell types are controlled. We and others recently showed that Sonic Hedgehog (Shh) signaling promotes the cortical RGC lineage switch to generate cortical oligodendrocytes and OB interneurons. During this process, cortical RGCs generate intermediate progenitor cells that express critical gliogenesis genes Ascl1, Egfr, and Olig2. The increased Ascl1 expression and appearance of Egfr+ and Olig2+ cortical progenitors are concurrent with the switch from excitatory neurogenesis to gliogenesis and OB interneuron neurogenesis in the cortex. While Shh signaling promotes Olig2 expression in the developing spinal cord, the exact mechanism for this transcriptional regulation is not known. Furthermore, the transcriptional regulation of Olig2 and Egfr has not been explored. Here, we show that in cortical progenitor cells, multiple regulatory programs, including Pax6 and Gli3, prevent precocious expression of Olig2, a gene essential for production of cortical oligodendrocytes and astrocytes. We identify multiple enhancers that control Olig2 expression in cortical progenitors and show that the mechanisms for regulating Olig2 expression are conserved between the mouse and human. Our study reveals evolutionarily conserved regulatory logic controlling the lineage switch of cortical neural stem cells.

Animals↗
PubMed1992

Drug design by machine learning: the use of inductive logic programming to model the structure-activity relationships of trimethoprim analogues binding to dihydrofolate reductase.

The machine learning program GOLEM from the field of inductive logic programming was applied to the drug design problem of modeling structure-activity relationships. The training data for the program were 44 trimethoprim analogues and their observed inhibition of Escherichia coli dihydrofolate reductase. A further 11 compounds were used as unseen test data. GOLEM obtained rules that were statistically more accurate on the training data and also better on the test data than a Hansch linear regression model. Importantly machine learning yields understandable rules that characterized the chemistry of favored inhibitors in terms of polarity, flexibility, and hydrogen-bonding character. These rules agree with the stereochemistry of the interaction observed crystallographically.

Artificial Intelligence↗
PubMed1996

Structure-activity relationships derived by machine learning: the use of atoms and their bond connectivities to predict mutagenicity by inductive logic programming.

We present a general approach to forming structure-activity relationships (SARs). This approach is based on representing chemical structure by atoms and their bond connectivities in combination with the inductive logic programming (ILP) algorithm PROGOL. Existing SAR methods describe chemical structure by using attributes which are general properties of an object. It is not possible to map chemical structure directly to attribute-based descriptions, as such descriptions have no internal organization. A more natural and general way to describe chemical structure is to use a relational description, where the internal construction of the description maps that of the object described. Our atom and bond connectivities representation is a relational description. ILP algorithms can form SARs with relational descriptions. We have tested the relational approach by investigating the SARs of 230 aromatic and heteroaromatic nitro compounds. These compounds had been split previously into two subsets, 188 compounds that were amenable to regression and 42 that were not. For the 188 compounds, a SAR was found that was as accurate as the best statistical or neural network-generated SARs. The PROGOL SAR has the advantages that it did not need the use of any indicator variables handcrafted by an expert, and the generated rules were easily comprehensible. For the 42 compounds, PROGOL formed a SAR that was significantly (P < 0.025) more accurate than linear regression, quadratic regression, and back-propagation. This SAR is based on an automatically generated structural alert for mutagenicity.

Algorithms↗
PubMed1998

Limit, logic, and computation.

We introduce "ultrafilter limits" into the classical Turing model of computation and develop a paradigm for interpreting the problem of distinguishing the class P from NP as a logical problem of decidability. We use P(NP) to denote decision problems which can be solved on a (nondeterministic) Turing machine in polynomial time. The concept is that in an appropriate limit it may be possible to prove that problems in P are still decidable, so a problem whose limit is undecidable would be established as lying outside of P.

Journal Article↗
PubMed2000

Small molecule developmental screens reveal the logic and timing of vertebrate development.

Much has been learned about vertebrate development by random mutagenesis followed by phenotypic screening and by targeted gene disruption followed by phenotypic analysis in model organisms. Because the timing of many developmental events is critical, it would be useful to have temporal control over modulation of gene function, a luxury frequently not possible with genetic mutants. Here, we demonstrate that small molecules capable of conditional gene product modulation can be identified through developmental screens in zebrafish. We have identified several small molecules that specifically modulate various aspects of vertebrate ontogeny, including development of the central nervous system, the cardiovascular system, the neural crest, and the ear. Several of the small molecules identified allowed us to dissect the logic of melanocyte and otolith development and to identify critical periods for these events. Small molecules identified in this way offer potential to dissect further these and other developmental processes and to identify novel genes involved in vertebrate development.

Animals↗
PubMed1996

Impact of working environments upon human-machine dialogues: a formal logic for the integrated specification of physical and cognitive ergonomic constraints on user interface design.

A range of techniques have been developed to improve the integration of computer systems into complex working environments. For instance, computer aided design tools can be used to simulate operators' posture at a particular workstation. Fitting studies can then be used to validate potential layouts. Unfortunately, few of these techniques can also be used to support the development of interactive dialogues. This is a critical problem for systems where designers must distribute application data amongst a number of different presentation devices. The position of these displays can be used to reflect the salience and priority of information. This paper presents techniques that support both user interface development and workstation layout. First order logic can be used to represent and reason about constraints on the design of human computer dialogues. The same formalism can also be used to identify appropriate locations for presentation devices within their working context; control rooms and offices. The findings of ergonomic studies can then be applied to analyze the mental and physical demands imposed by the interactive dialogues that are supported by particular devices. Unfortunately, formal specifications provide little impression of what it would be like to interact with a system within a particular environment. We have developed simulation tools to address this problem. Prototype displays can be presented within three dimensional models of their working context. The resulting simulations are directly derived from formal specifications and can be shown to members of concurrent design teams. They also provide a medium for communication with potential operators.

Computer Systems↗
PubMed1990

Acute gastrointestinal bleeding. A logical approach to management.

Management of acute gastrointestinal bleeding follows a logical sequence of steps. The first priority is to assess the magnitude of blood loss and resuscitate the patient. The patient history and nasogastric aspiration can help localize the source of bleeding to the upper tract or lower tract. Treatment of suspected upper gastrointestinal bleeding is usually empirical and consists of histamine 2 blockers (or sucralfate [Carafate]) or antacids. Diagnosis of the specific bleeding site is based on the severity, activity, and nature of the bleeding. Endoscopic and radiographic techniques may be useful. Intravenous vasopressin (Pitressin) therapy and endoscopic sclerotherapy are important in the management of variceal hemorrhage. Therapeutic endoscopic techniques are being used more often to manage nonvariceal bleeding as well.

Acute Disease↗