1,721,089 research outputs found
The sinusoidal traversable wormhole.
No full textIn a baby universe or the universe at a very small scale, the geometry of space-time is believed to exist as a foamy structure; a term called quantum foam first suggested by John Wheeler. This final year thesis report explores the properties of a sinusoidal traversable wormhole and attempts to solve for the existence of a safe geodesic on the wormhole that elementary particles are able to move about. The aim of this thesis is to achieve a safe geodesic elementary particles may travel on during the very beginning of the formation of the universe.
In this research I have managed to come out with a periodically safe geodesic which exists for one and a half cycle. This result is sufficient as the topology structure of the 'foamy' wormhole central to this research takes the shape of my sinusoidal wormhole, for half a cycle. For a minimum of one and a half period, the geodesic is guaranteed to be safe as it coils about the outer most region of the sinusoidal traversable wormhole.Bachelor of Science in Physic
Early warning signals for homoclinic bifurcation : the effectiveness of Lag-1 autocorrelation and variance, and the development of two novel techniques
No full textEarly warning signals (EWS) have been tested on many real-life systems to early detect bifurcations. In particular, the study of EWS for the homoclinic bifurcation is currently scarce and underdeveloped. Out of the several EWS, the effectiveness of the lag-1 autocorrelation and variance is tested in this thesis on theoretical systems exhibiting the saddle-node, hopf and homoclinic bifurcations. Our results show that their effectiveness varies across the board and neither of the two is a better EWS. In some cases, the behaviour of one EWS indicates an incoming bifurcation but the behaviour of the other indicates otherwise, and vice versa. In other cases, they falsely detect bifurcation when there is none. The limited success of the EWS on the homoclinic bifurcation motivated the development of two specific novel detection techniques, which are the minimum speed and curvature of the limit cycles near the saddle-point. Based on theoretical calculations, the minimum speed is expected to decrease towards zero as the system slows down near the saddle-point. On the other hand, the curvature is expected to increase towards infinity because a kink eventually forms at the saddle-point when homoclinic bifurcation is reached. Our results indeed show that as homoclinic bifurcation is approaching, the minimum speed and curvature tend towards zero and very large values.Bachelor of Science in Physic
Practical quantum cryptography : demonstration of secure commitments in the noisy storage model.
No full textThe establishment of quantum theory has sparked further advancements in computer
science and information theory. In this work, we explore aspects of quantum cryptography,
showing how physical assumptions combined with fundamental laws of nature allow
for secure communication, without additional computational assumptions as frequently
invoked in many present-day cryptographic protocols. These progresses have wide applications,
which can be used to perform tasks which lie in the central interest of modern
cryptography, such as secure identi cation of a customer to an ATM machine.
In particular, we have studied the bit commitment protocol within the scope of Noisy-
Storage Model, and proved its robustness against experimental errors, demonstrating the
feasibility of executing the protocol with real-world quantum devices. Having so, we
conducted the implementation with actual optical devices. On the technical aspect, we
developed a new set of uncertainty relations, which are extremely useful for actual implementations
of protocols. These relations allow a signi cant reduction in the amount of
classical information post-processing, directly shortening the computational time for secure
two-party protocols in the model. Our approach involves the analytical optimization
for a certain class of R enyi entropic measures conditioned on quantum measurements,
which might be of independent interest.Bachelor of Science in Physic
Multipole analysis on protein charge distribution.
No full textThe interactions in protein system are known to be very complicated. Extra attention should be paid to special cases where the interactions can be simplified such that the law of physics in proteins can be captured. A literature review on the protein force field was done so as to justify that the dominating guiding force is electrostatic effect. Therefore the focus of this project is on the guiding force in protein-protein / enzyme-substrate interaction.
The popular numerical methods in electrostatic potential calculation were summarized. The simplest calculation of electrostatic potential, i.e. using coulomb’s law of constant linear dielectric, was found to be ambiguous in protein system. Therefore the guiding force problem was tackled from the aspect of the charge distribution of the proteins.
The charge distribution in a protein is very complicated because it consists of thousands atoms bonded together. Multipole moments can provide a good insight to the charge distribution of a protein by giving simple patterns of the charge distribution as seen from a place far away from the protein. However, little study on charge distribution of protein by making use of its multipole moments has been done.
In this project, a programme used to calculate the multipole moments of proteins in both Cartesian and spherical coordinates was developed. It was applied to the study of charge distribution in secondary structures of protein. A simple toy model, ‘Secondary Structure Model’ (SSM), was built so that the charge distribution due to hydrogen bonds can be observed clearly and studied from the multipole moments. Simple patterns in the charge distribution of secondary structure were found in this model.
Besides, enzyme was also studied by calculating its multipoles. Cu-Zn Superoxide dismutase is an enzyme whose catalytic efficiency is found to be enhanced by electrostatic guiding force. Its multipole moments were found to be fluctuating among structures with the same amino acids sequence given in Protein Data Bank. Careful analysis had been done on the reliability of our partial charge parameter (AMBER) by comparing it against the other parameter set, CHARMM. Besides, we also checked on the structure alignment method and multipole calculation programme developed by ourselves. After excluding possible mistakes, we concluded that charged sidechain rotation can cause the fluctuations in multipole moments. This implies that charged sidechain rotation can cause observable charge distribution changes in protein.Bachelor of Science in Physic
Enhancement of entanglement by means of squeezing in continuous-variable systems
No full textIn this project, we investigate the enhancement of entanglement by means of local squeezing
of the coherent initial state in various two-mode coupled harmonic oscillator systems within
the pure Gaussian regime. Remarkably, we discover that the enhancement of maximum
entanglement produced in the time evolution occurs under two different conditions: the
existence or non-existence of an entanglement enhancement threshold. By developing a
mathematical framework, we are able to: (i) develop a phase-space picture that allows us
to explain the entanglement enhancement due to squeezing; (ii) explain the origin of the
threshold. In particular, it has enabled us to determine the analytical expression of the
threshold.Bachelor of Science in Physic
Impact of link-removal on the air transportation network.
No full textAs one of the critical infrastructure network, the air transportation network provides the fastest way for millions of people to travel around the world every day. At the same time, it is also responsible for the world-wide propagation of infectious diseases such as the influenza
and SARS. In this project, we study and analyze the worldwide air transportation network.
In particular, we will build a network which consists of more than 3000 airports and establish links between pairs of airports that are connected by non-stop passenger
flights. Then, the impact of link-removal on both the epidemic spreading and the centrality betweenness of the most central airports are investigated. Our result is that the link between Changi Airport and Newark Liberty International Airport, USA (SIN-EWK) and London Heathrow Airport, UK (SIN-LHR) are among the most suitable links for removal. We found that single link removal has no significant impact on reducing epidemic spreading on Changi Airport, Singapore.Bachelor of Science in Physic
Spatio-temporal modelling of population and urban mobility
No full textCrucial in the exchange of information, may it be tangible or not, is mobility.
From long-range migrations of populations to short-range movements in urban areas,
communities operate in the context of the networks of interactions they are embed-
ded in. The principal properties that de ne the attributes and evolution of systems
are in
uenced by their mobility networks regardless of scale in space and time. In
the long time scale of population migrations, we study the coevolution of languages
and genes spanning centuries.Doctor of Philosophy (SPMS
Evolutionary intelligence : a heuristic method of constructing conscious learning behavior and application to language development in infants
No full textThe topic of learning receives diverse perspectives in psychological cognitive and behavioral analysis. In this thesis, an evolutionary computational model is proposed to integrate both the cognitive and behavioral point of view. The constructed artificial intelligence (AI) was made to play Tic-Tac-Toe against experienced human opponents. The observed learning behavior of the AI, exhibited signs that could suggest ‘conscious learning’ behavior. This dialectic of learning is based on the hypothesis that learning is an evolutionary process (behavioral) mediated by certain internal memory organizing mechanism (cognitive). Genetic algorithm and cellular automaton are the two fundamental logic behind this model. Here in the game model, the AI is able to both successfully figure out rule(s) and strategies of the game. Adopting this approach, a simplified version of the AI is constructed to model infant language acquisition. In this infant model, we are able to mimic an infant’s initial phase of language development through the first three levels of consciousness via social interactions. This result could be of paramount importance in identifying infants with difficulty in acquiring language.Master of Scienc
Signatures of chaos in squeezed quantum kicked tops
No full textQuantum systems with the classical analogue in the chaotic region like kicked tops, have been found to experience enhancement in entanglement rates. The idea of spin squeezing is to reduce the quantum fluctuations in one component of the system at the sacrifice of increasing the other components. In this project, we have brought these two ideas together, by applying the quadratic squeeze operator on the quantum kicked top and measuring the entanglement of the system. Our results show that spin squeezing enhances the entanglement of kicked tops that are stable while reducing the entanglement of chaotic kicked tops. The hypothesis that we have come up with to explain this difference in the effect of entanglement is that the variance of the states are altered to a point where the initial state are no longer confined fully in the sea of chaos or stable island regions. We also proposed a new technique to enhance entanglement through periodic squeezing of the quantum kicked tops that are not fully chaotic. This results in the maximum entanglement achievable to be higher. We believe that these methods can be employed experimentally in order to improve and enhance entanglement in quantum systems.Bachelor of Science in Physic
Squeezing of spin ensemble
No full textQuantum mechanics has baffled generations of physicists due to its counterintuitive and bizarre predictions. Its manifestations include the Heisenberg uncertainty principle, quantisation of the electromagnetic (EM) field and its interaction with matter in quantum optics, bosonic and spin squeezing; all of which have no classical analogues. To probe the subtleties behind the coupled atom-field dynamics, the Jaynes-Cummings model (JCM) describing the matter-radiation interaction between a 2-level atom with a single cavity mode quantised EM field in a fixed number state, coherent state and squeezed coherent state is first studied separately. The JCM is next generalised for an N-atom system known as the Tavis-Cummings model (TCM) where the physics is now dominated by the collective behaviour of the atomic ensemble instead of the evolution of specific states. Lastly, the work undertaken by Bennett et al. to achieve spin squeezing via phonon-induced spin-spin interactions in diamond nanostructures coupled to a single mechanical mode of a nanoresonator is discussed to ascertain the possibility of squeezing within a spin ensemble with the experimental model described.Bachelor of Science in Physic
- …
