An algorithmic characterization of antimatroids

In an article entitled “Optimal sequencing of a single machine subject to precedence constraints” E.L. Lawler presented a now classical minmax result for job scheduling. In essence, Lawler's proof demonstrated that the properties of partially ordered sets were sufficient to solve the posed scheduling problem. These properties are, in fact, common to a more general class of combinatorial structures known as antimatroids, which have recently received considerable attention in the literature. It is demonstrated that the properties of antimatroids are not only sufficient but necessary to solve the scheduling problem posed by Lawler, thus yielding an algorithmic characterization of antimatroids. Examples of problems solvable by the general result are provided

Effect of Urea and Distillers Inclusion in Dry- Rolled Corn Based Diets on Heifer Performance and Carcass Characteristics

Crossbred heifers (n=96, BW = 810 ± 20) were utilized to evaluate the effects of increasing wet distillers grains plus solubles and urea inclusion in a dry rolled corn based finishing diet on performance and carcass characteristics. Heifers were individually fed using a calan gate system with a 2 × 2 factorial arrangement of treatments. Factors included distillers inclusion at either 10 or 20% of diet DM and urea inclusion at either 0.2 or 1.4% of diet DM. Th ere was no difference for final body weight, average daily gain, and feed conversion on a live or carcass adjusted basis for either urea or distillers inclusion in the diet. Dry matter intake was reduced with increased urea inclusion; however, distillers inclusion did not influence intake. Added distillers and urea in the diet had minimal impact on performance suggesting supplemental urea in a dry rolled corn based finishing diets is of minimal benefit when feeding at least 10% distillers grains

Phosphinic acid synthesis

Chapter 1 gives a background to the importance of phosphinic acids, and a description of their physical properties and chemical reactivity. A review of the more useful methods towards synthesis is given. At the end of the chapter, trivalent silyl phosphonite esters are introduced as potentially useful synthetic reagents. However, only limited work has performed using these species. Chapter 2 introduces the novel addition of bis(trimethylsilyl) phosphonite to c-unsaturated esters under basic silylating conditions. This reaction is optimised and transformed into a useful synthetic method for the preparation of phosphinic acids, named the "triethylammonium phosphinate reaction." Various other electrophiles were used as substrates in this reaction, little success was obtained. Theories are provided to explain side reactions and products, some additional reactions were performed to give evidence to support these theories. A novel reaction between a Nannich base and silyl phosphonite esters, yielding a phosphinic acid, is introduced. The problems of phosphinic acid purification by physical and chemical methods are discussed. Chapter 3 is concerned with the development of the "triethylammonium reaction" to allow addition of silyl phosphonite esters to a,-unsaturated ketones. The novel "sodium phosphinate" reaction was developed but little success was achieved, however excellent yields of phosphinic acids were obtained when a,-unsaturated esters were used as substrates. Chapter 4 is about developing a new reaction to allow phosphinic acid synthesis using vinyl ketones as substrates, under controlled conditions. This mild reaction was then combined with a novel method of purification forming adamantanammonium phosphinate esters. This flexible methodology was established by the preparation of a variety of substituted phosphinic acids and phosphinate esters. In chapter 5 adaption of the reaction discovered in chapter 4 was undertaken which, allows the synthesis of phosphinic acids using alkyl iodides. A useful reaction was developed which gives similar products to the Arbuzov reaction, however it is demonstrated that this new reaction does not proceed by the same mechanism. Chapter 6 gives an account of work undertaken to the phosphinate analogue of platelet activating factor. The original route was unsuccessful, reasons for this are discussed. A shorter alternative route is given, which relies on chemistry developed in this thesis. I have made an attempt to show the utility of the novel methodology contained in this thesis, by giving my ideas on proposed routes to the synthesis of some interesting phosphinate analogues. I consider some of these analogues to be useful biochemical tools

The common C-terminal sequences of substance P and neurokinin A contact the same region of the NK-1 receptor

AbstractAlthough neurokinin A (NKA), a tachykinin peptide with sequence homology to substance P (SP), is a weak competitor of radiolabeled SP binding to the NK-1 receptor (NK-1R), more recent direct binding studies using radiolabeled NKA have demonstrated an unexpected high-affinity interaction with this receptor. To document the site of interaction between NKA and the NK-1R, we have used a photoreactive analogue of NKA containing p-benzoyl-L-phenylalanine (Bpa) substituted in position 7 of the peptide. Peptide mapping studies of the receptor photolabeled by 125I-iodohistidyl1-Bpa7NKA have established that the site of photoinsertion is located within a segment of the receptor extending from residues 178 to 190 (VVCMIEWPEHPNR). We have previously shown that 125I-BH-Bpa8SP, a photoreactive analogue of SP, covalently attaches to M181 within this same receptor sequence. Importantly, both of these peptides (125I-iodohistidyl1-Bpa7NKA and 125I-BH-Bpa8SP) have the photoreactive amino acid in an equivalent position within the conserved tachykinin carboxyl-terminal tail. In this report, we also show that site-directed mutagenesis of M181 to A181 in the NK-1R results in a complete loss of photolabeling of both peptides to this receptor site, indicating that the equivalent position of SP and NKA, when bound to the NK-1R, contact the same residue

Effect of Urea and Distillers Inclusion in Dry- Rolled Corn Based Diets on Heifer Performance and Carcass Characteristics

Crossbred heifers (n=96, BW = 810 ± 20) were utilized to evaluate the effects of increasing wet distillers grains plus solubles and urea inclusion in a dry rolled corn based finishing diet on performance and carcass characteristics. Heifers were individually fed using a calan gate system with a 2 × 2 factorial arrangement of treatments. Factors included distillers inclusion at either 10 or 20% of diet DM and urea inclusion at either 0.2 or 1.4% of diet DM. Th ere was no difference for final body weight, average daily gain, and feed conversion on a live or carcass adjusted basis for either urea or distillers inclusion in the diet. Dry matter intake was reduced with increased urea inclusion; however, distillers inclusion did not influence intake. Added distillers and urea in the diet had minimal impact on performance suggesting supplemental urea in a dry rolled corn based finishing diets is of minimal benefit when feeding at least 10% distillers grains

Narrow Line Cooling: Finite Photon Recoil Dynamics

We present an extensive study of the unique thermal and mechanical dynamics for narrow-line cooling on the 1S0 - 3P1 88Sr transition. For negative detuning, trap dynamics reveal a transition from the semiclassical regime to the photon-recoil-dominated quantum regime, yielding an absolute minima in the equilibrium temperature below the single-photon recoil limit. For positive detuning, the cloud divides into discrete momentum packets whose alignment mimics lattice points on a face-centered-cubic crystal. This novel behavior arises from velocity selection and "positive feedback" acceleration due to a finite number of photon recoils. Cooling is achieved with blue-detuned light around a velocity where gravity balances the radiative force.Comment: 4 pages, 3 figures, Phys. Rev. Lett., in pres

Better Bell Inequality Violation by Collective Measurements

The standard Bell inequality experiments test for violation of local realism by repeatedly making local measurements on individual copies of an entangled quantum state. Here we investigate the possibility of increasing the violation of a Bell inequality by making collective measurements. We show that nonlocality of bipartite pure entangled states, quantified by their maximal violation of the Bell-Clauser-Horne inequality, can always be enhanced by collective measurements, even without communication between the parties. For mixed states we also show that collective measurements can increase the violation of Bell inequalities, although numerical evidence suggests that the phenomenon is not common as it is for pure states.Comment: 7 pages, 4 figures and 1 table; references update

Quantum Control of a Single Qubit

Measurements in quantum mechanics cannot perfectly distinguish all states and necessarily disturb the measured system. We present and analyse a proposal to demonstrate fundamental limits on quantum control of a single qubit arising from these properties of quantum measurements. We consider a qubit prepared in one of two non-orthogonal states and subsequently subjected to dephasing noise. The task is to use measurement and feedback control to attempt to correct the state of the qubit. We demonstrate that projective measurements are not optimal for this task, and that there exists a non-projective measurement with an optimum measurement strength which achieves the best trade-off between gaining information about the system and disturbing it through measurement back-action. We study the performance of a quantum control scheme that makes use of this weak measurement followed by feedback control, and demonstrate that it realises the optimal recovery from noise for this system. We contrast this approach with various classically inspired control schemes.Comment: 12 pages, 7 figures, v2 includes new references and minor change