Contemporary Physics

The following sections are included:

• Preface

• COMMITTEES

• LIST OF SPEAKERS

• Contents

The following sections are included:

• Early history of application of X-rays in biology

• Synchrotron radiation

• Applications of synchrotron radiation in macromolecular crystallography
  • Achievements
  • Drug design
  • Future

• Other applications of synchrotron radiation in biology

• Non-crystalline diffraction

• Circular dichroism

• Infrared Microspectroscopy

• Soft X-ray imaging

• Medical beam lines

• Concluding remarks

It is a great pleasure to thank Professor Riazuddin for inviting me to this symposium which is held on the occasion of the inauguration of the new National Centre for Physics. We all should congratulate him for this great achievement which will be so beneficial both for international cooperation and for the strengthening of science in Pakistan.

At present there are more than 50 synchrotron radiation light source research facilities in operation in 19 countries around the world, with more in construction and design (see www.lightsources.org). Although most facilities are in technologically advanced countries, there is significant activity in the developing world. Twenty to thirty years ago several developing countries (Brazil, China, India, Korea, and Taiwan) began light source projects. These have now been completed and have been in operation for about 10 or more years. More recently a light source has started operation in Thailand (http://www.nsrc.or.th/Eng/index. htm). In this paper we describe the benefits that operating synchrotron light source facilities in developing countries have had…

In quantum information processing and quantum computing protocols information is encoded in the state of a quantum system. After processing the information it has to be read out what is equivalent to determining the final state of the system. When the possible final states are not orthogonal this is a highly nontrivial task that constitutes the general area of what is known as quantum state discrimination. It consists in finding measurement schemes that, according to some figure of merit, will determine the state of the system. Optimized measurement schemes often lead to generalized measurements (Positive Operator Valued Measures, POVMs). In this tutorial review we illustrate the power of the POVM concept on examples relevant to applications in quantum cryptography. In order to keep the flow of the presentation we give a brief introduction to the theory of generalized measurements in an appendix.

The direct electrical interfacing of semiconductor chips with individual nerve cells and with brain tissue is considered. At first, the structure of the cell-chip contact is described and then the electrical coupling is characterized between ion channels, the electrical elements of nerve cells, and transistors and capacitors of silicon chips. On that basis the signal transmission between microelectronics and the microionics of nerve cells is implemented in both directions. Simple hybrid neuroelectronic systems are assembled with neuron pairs and small neuronal networks. Finally, the interfacing is extended to brain tissue. The application of CMOS chips with recording and stimulation sites allows an imaging of neuronal activity with high spatiotemporal resolution. Goal of the work in an integration of neuronal network dynamics and digital electronics on a microscopic level for applications in brain research, medical prosthetics and information technology.

We briefly summarize the use of Gauss sums to factor numbers and propose an NMR realization of exponential sums.

Physics is a seamless dialogue with Nature that transcends the divisions made by practising physicists—often for convenience, often imposed by their own limitations. It is difficult to sustain the notion that one branch of physics can satisfactorily answer all the questions of Nature. I expand on this theme briefly, and also technically, using the example of hydrodynamic turbulence.

We present simulation studies of the formation and dynamics of dark solitons and vortices, and of nonlinear interactions between intense circularly polarized electromagnetic (CPEM) waves and electron plasma oscillations (EPOs) dense in quantum electron plasmas. The electron dynamics in the latter is governed by a pair of equations comprising the nonlinear Schrödinger and Poisson system of equations, which conserves electrons and their momentum and energy. The dynamics of the CPEM waves is also governed by a nonlinear schrödinger equation, which is nonlinearly coupled with the nonlinear Schrödinger equation of the EPOs via the relativistic ponderomotive force, the relativistic electron mass increase in the CPEM field, and the electron density fluctuations. The present governing equations in one spatial dimension admit stationary solutions in the form a dark envelope soliton. The dynamics of the latter reveals its robustness. Furthermore, we numerically demonstrate the existence of cylindrically symmetric two-dimensional quantum electron vortices, which survive during collisions. The nonlinear equations admit the modulational instability of an intense CPEM pump wave against EPOs, leading to the formation and trapping of localized CPEM wave pipes in the electron density hole that is associated with a positive potential distribution in our dense plasma.

The Lagrangian for collective (fluid-mechanical) matter-field coupling must incorporate a non-canonical structure that is symbolized by the nonzero “vorticity” of the momentum (violating the basic Hamilton-Jacobi relation P = ∇S for the momentum P and the action S). The Eulerian view of the mechanics, describing the dynamics in terms of “synchronic” variables, reveals the topological defects of the Poisson bracket, which are represented by the so-called “Casimir invariants”. Adding Casimir invariants, one may transform the Hamiltonian without changing the dynamics. The critical points of the transformed Hamiltonian describes multi-scale matter-field couplings.

Nanoparticles of bimetallic alloys have been shown to possess composition dependent characteristics which distinguish themselves from the corresponding bulk alloys. Taking the 34-atom nanoalloy of Ag and Cu (Ag₂₇Cu₇), we show using first principles electronic structure calculations that this core-shell alloy indeed has perfect D_5h symmetry and consists of only 6 non-equivalent (2 Cu and 4 Ag) atoms. Analysis of the interatomic bond lengths and detailed electronic structure further reveal that the Cu atoms play a major role in controlling the characteristics of the nanoalloy. The higher cohesive energy, together with shorter bond length for Cu, compared to Ag, conspire to produce a hierarchy in the relative strengths of the Ag – Cu, Ag – Ag, and Cu – Cu bonds and corresponding interatomic bond lengths, point to the uniqueness in the characteristics of this nanoalloy. Charge density plots of Ag₂₇Cu₇ provide further insights into the relative strengths of the various interatomic bonds.

In response to skyrocketing fuel costs and evidence of climate change, real technological progress is needed towards harnessing the clean power from the sun to drive human progress. Here we present two approaches to harnessing solar energy currently under investigation in our group. One involves novel photovoltaic cells using different sized quantum dots. Another uses proven photocatalysts to directly electrolyze water, producing hydrogen. The technological background will be discussed, as well as current state of the art and future research direction.

We review the salient features of B-meson physics, with particular emphasis on the measurements carried out at the B-factories and Tevatron, theoretical progress in understanding these measurements in the context of the standard model, and anticipation at the LHC. Topics discussed specifically are the current status of the Cabibbo-Kobayashi-Maskawa matrix, the CP-violating phases, rare radiative and semileptonic decays, and some selected non-leptonic two-body decays of the B mesons.

We give an overview of some of the ideas involved in formulating a quantum theory of gravity, such as fundamental discreteness of spacetime and background independent quantization We describe the role played by these ingredients in understanding gravitational collapse in quantum gravity.

One could call 2006 as the year of cosmology since in that year two US scientists were awarded the Nobel prize for their studies of the Cosmic Microwave Background (CMB) spectrum and anisotropy. Here I recall earlier studies of the CMB anisotropy done with the Soviet spacecraft Prognoz-9 by the Relikt-1 team. Problems of modern cosmology are outlined. We discuss conformal cosmology parameters from supernovae data in brief. Two approaches to solve the basic problems of cosmology, such as dark matter and dark energy, are discussed, the first (standard) possibility is to introduce new particles, fields etc; the second possibility is to try to change the law of gravity to fit observational data. We discuss advantages and disadvantages of the second choice.

The following sections are included:

• List of Participants