Geometry and the anomalous Hall effet in ferromagnets

The geometric ideas underlying the Berry phase and the modern viewpoint of Karplus and Luttinger's theory of the anomalous Hall effect are discussed in an elementary way. We briefly review recent Hall and Nernst experiments which support the dominant role of the KL velocity term in ferromagnets.Comment: 6 pages, 4 figures, conference proceedings, tutorial revie

Phase fluctuations versus Gaussian fluctuations in optimally-doped YBa2_2Cu3_3O7_7

We analyze recent torque measurements of the magnetization $M_d$ vs. magnetic field $H$ in optimally doped YBa$_2$Cu$_3$O$_{7-y}$ (OPT YBCO) to argue against a recent proposal by Rey et al that the magnetization results above $T_c$ are consistent with Gaussian fluctuations. We find that, despite its strong interlayer coupling, OPT YBCO displays an anomalous non-monotonic dependence of $M_d$ on $H$ which represents direct evidence for the locking of the pair wavefunction phase $\theta_n$ at $T_c$ and the subsequent unlocking by a relatively weak $H$. These unusual features characterize the unusual nature of the transition to the Meissner state in cuprate superconductors. They are absent in low-$T_c$ superconductors to our knowledge. We also stress the importance of the vortex liquid state, as well as the profiles of the melting field $H_m(T)$ and the upper critical field curve $H_{c2}(T)$ in the $T$-$H$ plane. Contrary to the claims of Rey et al, we show that the curves of the magnetization and the Nernst signal illustrate the inaccessibility of the $H_{c2}$ line near $T_c$. The prediction of the $H_{c2}$ line by Rey et al is shown to be invalid in OPT YBCO.Comment: 6 pages, 6 figure

Distance learning of engineering based subjects: A case study.

YesWith the advancement of technology, significant changes have been introduced into the learning and teaching environment. The importance of enhancing the interest of learners is an on-going challenge for educators of all levels. In this respect, teaching and learning practices are adapting to students¿ exposure to technological and social trends. In this presentation, a case study of using technology to enhance the learners¿ environment for engineering-based subjects in higher education is presented. The approach consists of delivering interactive materials through a Virtual Learning Environment and integrating web application technologies to enhance the learners¿ experience. Due to the vast subject areas in engineering and the variety of content of each subject, a general methodology is first identified and adopted. This consists of stages that show the progress from initial development to deployment of the materials, followed by evaluation of the module and further improvements carried out on the module based on qualitative evaluation. The evaluation process consists of the application of electronic surveys for feedback on the distance learning module. In addition, monitoring of the students¿ usage of the materials is also carried out. The presentation concludes with the presentation of the initial results from a current e-learning module

The zero-energy state in graphene in a high magnetic field

The fate of the charge-neutral Dirac point in graphene in a high magnetic field $H$ has been investigated at low temperatures ($T\sim$ 0.3 K). In samples with small $V_0$ (the gate voltage needed to access the Dirac point), the resistance $R_0$ at the Dirac point diverges steeply with $H$, signalling a crossover to an insulating state in intense field. The approach to the insulating state is highly unusual. Despite the steep divergence in $R_0$, the profile of $R_0$ vs. $T$ in fixed $H$ saturates to a $T$-independent value below 2 K, consistent with charge carrying gapless excitations.Comment: 4 pages, 4 figures. Four new sub-figures have been added. Text expanded to discuss data from more sample

An Examination of Embryogenic and Non-Embryogenic Cultures of Oil Palm (Elaeis Guineensis Jacq.)

Somatic embryogenesis of crop plants such as oil palm has generated considerable research interest. However, the main obstacle that hinders the development of an economically viable propagation system is the low frequency of embryogenesis. Currently, most local tissue culture laboratories are reporting embryogenesis rates of approximately 6%. Due to the lack of knowledge about oil palm somatic embryogenesis, it would be difficult to understand or even to attempt to improve the process. Hence, this study has been tailored to understand the fundamental processes that could occur during embryogenesis by analyzing differences between embryogenic (BC) and non-embryogenic (NEC) in vitro cultures of oil palm. The initial studies concentrated on elucidating the differences found between EC and NEC at the microscopical level. Proembryo (PE) structures were predominantly found in ECs. The phenomenon of isolation of cells, as a prerequisite to embryogenesis, was observed in the formation of PEs. It was hypothesized that the surrounding cells at the periphery of each PE structure could have gone through programmed cell death (PCD) hence creating the condition of 'isolation of cells'.The hypothesis that PCD could play an important role in the embryogenesis process was further supported by studies carried out at the physiological and molecular level. ECs were found to be metabolically more active than NECs, thus indicating that ECs would need an efficient system to overcome the accumulation of reactive oxygen species (ROS), a toxic byproduct of aerobic metabolism. With the isolation of the embryogenic tissue specific OPEml, which encodes for an antioxidant known as peroxiredoxin, it is believed that it functions by protecting the proembryos from being damaged by the ROS but killing the cells surrounding them. OPEml represents the first peroxiredoxin to be isolated from a palm and has potential to be exploited as a molecular marker for embryogenic potential of in vitro cultures. In addition to this, with the knowledge of the physiological state of embryogenic and non-embryogenic cultures, a non-destructive method for the detection of embryogenic potential can now be devised by taking advantage of the reaction mechanism of oxidative dyes in culture media.Besides this, attempts were also made to isolate other embryogenic related genes by means of a rapid cloning method for differentially expressed cDNAs. This technique is better known as Suppression Subtractive Hybridization. Out of a total 595 clones screened, only 66 were found to be embryogenic specific. Amongst these clones, one of them was characterized and shown to be closely related to a class IV chitinase EP3. This clone was designated as OPSSHI. There is some evidence to suggest from the northern analysis study, that different subsets of class IV endochitinase EP3 were being detected, as two differently sized transcripts were observed. It is possible that they encode proteins that have differing functions. However, due to the generally short fragments being produced through this technique, it is still too early to propose a functional role for endochitinase(s) in the oil palm system

Anomalous thermopower and Nernst effect in CeCoIn5\rm CeCoIn_5: entropy-current loss in precursor state

The heavy-electron superconductor CeCoIn$_5$ exhibits a puzzling precursor state above its superconducting critical temperature at $T_c$ = 2.3 K. The thermopower and Nernst signal are anomalous. Below 15 K, the entropy current of the electrons undergoes a steep decrease reaching $\sim$0 at $T_c$. Concurrently, the off-diagonal thermoelectric current $\alpha_{xy}$ is enhanced. The delicate sensitivity of the zero-entropy state to field implies phase coherence over large distances. The prominent anomalies in the thermoelectric current contrast with the relatively weak effects in the resistivity and magnetization.Comment: 5 figures, 4 page