Very low energy electron microscopy of graphene flakes

Commercially available graphene samples are examined by Raman spectroscopy and very low energy scanning transmission electron microscopy. Limited lateral resolution of Raman spectroscopy may produce a Raman spectrum corresponding to a single graphene layer even for flakes that can be identified by very low energy electron microscopy as an aggregate of smaller flakes of various thicknesses. In addition to diagnostics of graphene samples at larger dimensions, their electron transmittance can also be measured at very low energies.

The validity and reliability of iridology in the diagnosis of previous acute appendicitis as evi-denced by appendectomy

Iridology is defined as a photographic science that identifies pathological and functional changes within organs via biomicroscopic iris assessment for aberrant lines, spots, and discolourations. According to iridology, the iris does not reflect changes  during  anaesthesia,  due  to  the  drugs inhibitory  effects  on  nerves  impulses,  and  in cases of organ removal, it reflects the pre-surgical condition.The profession of Homoeopathy is frequently associated with iridology and in a recent survey (2009)  investigating  the  perceptions  of  Masters of  Technology  graduates  in  Homoeopathy  of University of Johannesburg, iridology was highly regarded as a potential additional skill requirement for assessing the health status of the patient.This  study  investigated  the  reliability  of iridology  in  the  diagnosis  of  previous  acute appendicitis, as evidenced by appendectomy. A total of 60 participants took part in the study. Thirty of the 60 participants had an appendectomy due to acute appendicitis, and 30 had had no prior history  of  appendicitis.  Each  participant’s  right iris  was  documented  by  photography  with  the use  of  a  non-mydriatic  retinal  camera  that  was reset for photographing the iris. The photographs were then randomized by an external person and no identifying data made available to the three raters.  The  raters  included  the  researcher,  who had little experience in iridology and two highly experienced  practising  iridologists.  Data  was obtained  from  the  analyses  of  the  photographs wherein  the  presence  or  absence  of  lesions (implying acute appendicitis) was indicated by the raters. None of the three raters was able to show a significant  success  rate  in  identifying  correctly the  people  with  a  previous  history  of  acute appendicitis and resultant appendectomies from those  who  had  no  previous  history  of  acute appendicitis.  Therefore the outcome of this study indicated an outcome that was subject to chance.The  null  hypothesis  that  states  that appendectomy due to acute appendicitis does not manifest in corresponding lesions in the iris, is supported. It is in the opinion of the researchers that the  association  of  iridology  with  homoeopathic practice may harm the credibility of the profession and that further research on iridology is needed to disprove this conviction. (S Afr Optom 2013 72(3) 127-132)

A topological paradigm for hippocampal spatial map formation using persistent homology

An animal's ability to navigate through space rests on its ability to create a mental map of its environment. The hippocampus is the brain region centrally responsible for such maps, and it has been assumed to encode geometric information (distances, angles). Given, however, that hippocampal output consists of patterns of spiking across many neurons, and downstream regions must be able to translate those patterns into accurate information about an animal's spatial environment, we hypothesized that 1) the temporal pattern of neuronal firing, particularly co-firing, is key to decoding spatial information, and 2) since co-firing implies spatial overlap of place fields, a map encoded by co-firing will be based on connectivity and adjacency, i.e., it will be a topological map. Here we test this topological hypothesis with a simple model of hippocampal activity, varying three parameters (firing rate, place field size, and number of neurons) in computer simulations of rat trajectories in three topologically and geometrically distinct test environments. Using a computational algorithm based on recently developed tools from Persistent Homology theory in the field of algebraic topology, we find that the patterns of neuronal co-firing can, in fact, convey topological information about the environment in a biologically realistic length of time. Furthermore, our simulations reveal a "learning region" that highlights the interplay between the parameters in combining to produce hippocampal states that are more or less adept at map formation. For example, within the learning region a lower number of neurons firing can be compensated by adjustments in firing rate or place field size, but beyond a certain point map formation begins to fail. We propose that this learning region provides a coherent theoretical lens through which to view conditions that impair spatial learning by altering place cell firing rates or spatial specificity.

Bioluminescent signal system: bioluminescence immunoassay of pathogenic organisms

The Ca(2+)-regulated photoprotein obelin has been examined as a label for bioluminescence immunoassay of infective agents. The hepatitis B virus (HbsAg) and the bacteria Escherichia coli and Shigella sonnei lipopolysaccharide (LPS) were chosen as model antigens. Chemically synthesized obelin-corresponding antibody conjugates were used in a solid-phase microplate immunoassay. The sensitivities achieved by the assay were 0.25 ng/mL for S. sonnei LPS and 0.375 ng/mL for HbsAg. A novel, filter-based immunoassay to determine bacterial admixtures in the environment was proposed. The NanoCeram filters were effectively applied to 'trap' and pre-concentrate pathogens from samples under study for the purposes of further detection and measurement of the absorbed material by bioluminescence immunoassay.

Corrections of magnification and focusing in a cathode lens-equipped scanning electron microscope

One of the well-proven and efficient methods of obtaining a very low-energy impact of primary electrons in the scanning electron microscope is to introduce a retarding field element below the pole piece of the objective lens (OL). It is advantageous to use the specimen alone as the negatively biased electrode (i.e., cathode of the cathode lens). The optical power of the cathode lens modifies some of the standard parameters of the image formation such as relation of working distance to OL excitation or magnification to the scanning coils current, the impact angle of primary electrons, and so forth. In computer-controlled electron microscopes these parameters, particularly with regard to focusing and magnification, can be corrected automatically. Derivation of algorithms for such corrections and their experimental verifications are presented in this paper. Furthermore, a more accurate analytical expression for the focal length of an aperture lens is derived.