Differential equations with soliton behaviour

Various non-linear wave equations are found to possess solitons - stable solitary waves which only undergo a change of position on collision with each other. It is shown in chapter 1, how the various soliton properties of the sine-Gordon equation, u(_xy) = F(u) sin u, May be derived from its Backlund Transformation. Most of the rest of the thesis consists of several attempts to find Backlund Transformations for other equations of the form u = F(u) by generalizing the usual form of the Backlund Transformation. The only exception to this is in chapter 2 where equations of the form u(_xy) = A(x,y,u).u(_x) + B(x,y,u).u(_y) + C(x,y,u) are considered. The rest of chapter 2 considers the effect of allowing the Backlund Transformation to depend explicitly on the independent variables or on integrals of the dependent variables. The rest of this thesis concentrates on allowing the Backlund Transformation to depend on derivatives only of the "old" and "new" variables, u and u'. It is found that if u and u' satisfy u(_xy) = F(u) where F'''(u) = K.F''(u) and F''(u) = K.F(u) then there are no Backlund Transformations of the following form. Chapter 3. u’(_x) = P(u,u';p(_1),.., ,P(_N);q(_1),...,q(M)) u;(_y)= Q(u,u';p(_1),...,P(_N);q(_1),...,q(_M)) except possibly when M = 1 , N > 7 and F(u) = A(_1).e(^cu) + A(_2).e(^-2cu). Chapter 4. u’(_xx) = P(u, u’, u(_x), u’(_x), x(_y), u(_xx), u(_yy) u’(_y) = Q(u, u’, u(_x), u’(_x), x(_y), u(_xx), u(_yy) Chapter 5 (^1)/(_2) (p’(_N+1) p(_N+1) – P(P(_0), P(_1),…,P(_N);P’(_0),…,P’(_N) N <5 (^1)/(_2)(q’ +q) = Q(P(_0), P(_1),…,P(_N);P(_0),…,P’(_N

The Spirit Lives On: Communication Seminars as a Surprisingly Hardy, Valuable, and Promising Heritage of NPAC

After many decades, dwindling numbers of communicators, extension personnel, and development professionals recall the National Project in Agricultural Communications (NPAC) of the 1950s and early 1960s. But around the world many professionals, scholars, and organizations can recognize the spirit and legacy of NPAC, which has had substantial impact well beyond its original national mission. NPAC became the springboard for a long-running series of communication seminars that built the capacity of foreign students, studying in the United States, to return home better able to communicate as change agents in fostering development. Seminars of NPAC also point to key ingredients for addressing urgent issues facing our nation and world today. This study addresses the origins, features, transitions, durability, and impacts of those communication seminars across nearly 60 years. The authors used historical analysis to reveal a surprising trail of service that leads to the present day and beyond. It provides new insights about how the NPAC communication training program has exerted more than 15 kinds of impact on agricultural development, on organizations at all levels throughout the world - and on individuals touched by it. The analysis highlights insightful, unpublished backstories about the communication training heritage of NPAC. It also identifies key elements of effective communication training programs and identifies opportunities for further research and practice. It could help readers identify professional development innovations the Journal of Applied Communications will advance and report during its second century

Studies of geometric wakefields and impedances due to collimators

In this note we study the geometric wakefields generated by a driving electron bunch in the SPARC LAB COMB chamber. Due to the change in iris radius of the beam pipe leading into the chamber, the electron beam will induce wakefields, which can have an effect on the bunches in the train used for the SL COMB experiment. Here, we present wakefields and impedances simulations and determine the effects that they may have on the beam properties

Microbunching and Coherent Synchrotron Radiation in Linear Free Electron Lasers

The optimal performance of short-wavelength free-electron lasers (FELs), driven by high-energy bunches of electrons, is limited by collective interactions that occur due to the self-fields of particles within the bunch. An understanding of these collective effects is therefore crucial for current and future machines. In particular, it is important when designing and operating such a machine that these effects are understood, and mitigated as much as possible. In order to achieve such an understanding, a correspondence between the theory of the impact of these collective effects, their calculation using computer-based simulation codes, and experimental measurements of the effects, is essential. This thesis presents a study of two such collective effects: coherent synchrotron radiation (CSR) and the microbunching instability. An extension to the 1D theory of CSR is derived, which correctly takes account of effects arising due to the electron bunch entering and exiting a bending magnet. Theoretical predictions of these CSR transient effects are then compared with results from simulation codes. The CSR-induced emittance growth is then studied experimentally in the FERMI FEL across a range of electron bunch parameters, showing good agreement between theory, simulation and experiment in most cases, and some divergence during more extreme bunch compression scenarios. In addition, the microbunching instability in the FERMI FEL has been studied extensively. A new method of characterising the instability using 2D Fourier analysis has been developed, which uncovers previously unseen parameters, and demonstrates the necessity of performing a thorough analysis in order to understand fully this effect. The microbunching instability has also been induced, by imposing periodic modulations on electron bunches across a number of accelerator lattice configurations. Comparisons between theory, simulation and experiment are also shown in this case, demonstrating an improved understanding of the development of these collective effects

Crystallographic Studies of Two Bacterial AntibioticResistance Enzymes: Aminoglycoside Phosphotransferase (2')-Ic and GES-1\beta-lactamase

Guiana Extended-Spectrum-1 (GES-1) and Aminoglycoside phosphotransferase (2')-Ic (APH(2')-Ic) are two bacteria-produced enzymes that essentially perform the same task: they provide resistance to an array of antibiotics. Both enzymes are part of a growing resistance problem in the medical world. In order to overcome the ever-growing arsenal of antibiotic-resistance enzymes, it is necessary to understand the molecular basis of their action. Accurate structures of these proteins have become an invaluable tool to do this. Using protein crystallography techniques and X-ray diffraction, the protein structure of GES-1 bound to imipenem (an inhibitor) has been solved. Also, APH(2')-Ic has been successfully crystallized, but its structure was unable to be solved using molecular replacement using APH(2')-Ib as a search model. The structure of GES-1, with bound imipenem was solved to a resolution of 1.89A, and though the inhibitor is bound with only moderate occupancy, the structure shows crucial interactions inside the active site that render the enzyme unable to complete the hydrolysis of the {beta}-lactam ring. The APH(2')-Ic dataset could not be matched to the model, APH(2')-Ib, with which it shares 25% sequence identity. The structural information gained from GES-1, and future studies using isomorphous replacement to solve the APH(2')-Ic structure can aid directly to the creation of novel drugs to combat both of these classes of resistance enzymes

Mutations in the gene for the granulocyte colony-stimulating-factor receptor in patients with acute myeloid leukemia preceded by severe congenital neutropenia

BACKGROUND. In severe congenital neutropenia the maturation of myeloid progenitor cells is arrested. The myelodysplastic syndrome and acute myeloid leukemia develop in some patients with severe congenital neutropenia. Abnormalities in the signal-transduction pathways for granulocyte colony-stimulating factor (G-CSF) may play a part in the progression to acute myeloid leukemia. METHODS. We isolated genomic DNA and RNA from hematopoietic cells obtained from two patients with acute myeloid leukemia and histories of severe congenital neutropenia. The nucleotide sequences encoding the cytoplasmic domain of the G-CSF receptor were amplified by means of the polymerase chain reaction and sequenced. Murine myeloid 32D.C10 cells were transfected with complementary DNA encoding the wild-type or mutant G-CSF receptors and tested for their responses to G-CSF. RESULTS. Point mutations in the gene for the G-CSF receptor were identified in both patients. The mutations, a substitution of thymine for cytosine at the codon for glutamine at position 718 (Gln718) in one patient and at the codon for glutamine at position 731(Gln731) in the other, caused a truncation of the C-terminal cytoplasmic region of the receptor. Both mutant and wild-type genes for the G-CSF receptor were present in leukemic cells from the two patients. In one patient, the mutation was also found in the neutropenic stage, before the progression to acute myeloid leukemia. The 32D.C10 cells expressing mutant receptors had abnormally high proliferative responses but failed to mature when cultured in G-CSF. The mutant G-CSF receptors also interfered with terminal maturation mediated by the wild-type G-CSF receptor in the 32D.C10 cells that coexpressed the wild-type and mutant receptors. CONCLUSIONS. Mutations in the gene for the G-CSF receptor that interrupt signals required for the maturation of myeloid cells are involved in the pathogenesis of severe congenital neutropenia and associated with the progression to acute myeloid leukemia

Developments in CLARA accelerator design and simulations

We present recent developments in the accelerator design of CLARA (Compact Linear Accelerator for Research and Applications), the proposed UK FEL test facility at Daresbury Laboratory. Updates on the electron beam simulations and code comparisons including wakefields are described. Simulations of the effects of geometric wakefields in the small-aperture FEL undulator are shown, as well as further simulations on potential FEL experiments using chirped beams. We also present the results of simulations on post-FEL diagnostics