Speed of processing in the primary motor cortex: A continuous theta burst stimulation study

‘Temporally urgent’ reactions are extremely rapid, spatially precise movements that are evoked following discrete stimuli. The involvement of primary motor cortex (M1) and its relationship to stimulus intensity in such reactions is not well understood. Continuous theta burst stimulation (cTBS) suppresses focal regions of the cortex and can assess the involvement of motor cortex in speed of processing. The primary objective of this study was to explore the involvement of M1 in speed of processing with respect to stimulus intensity. Thirteen healthy young adults participated in this experiment. Behavioral testing consisted of a simple button press using the index finger following median nerve stimulation of the opposite limb, at either high or low stimulus intensity. Reaction time was measured by the onset of electromyographic activity from the first dorsal interosseous (FDI) muscle of each limb. Participants completed a 30 min bout of behavioral testing prior to, and 15 min following, the delivery of cTBS to the motor cortical representation of the right FDI. The effect of cTBS on motor cortex was measured by recording the average of 30 motor evoked potentials (MEPs) just prior to, and 5 min following, cTBS. Paired t-tests revealed that, of thirteen participants, five demonstrated a significant attenuation, three demonstrated a significant facilitation and five demonstrated no significant change in MEP amplitude following cTBS. Of the group that demonstrated attenuated MEPs, there was a biologically significant interaction between stimulus intensity and effect of cTBS on reaction time and amplitude of muscle activation. This study demonstrates the variability of potential outcomes associated with the use of cTBS and further study on the mechanisms that underscore the methodology is required. Importantly, changes in motor cortical excitability may be an important determinant of speed of processing following high intensity stimulation.

Community structure, diversity and spatial organization of enchytraeids in Mediterranean urban holm oak stands

There is a strong northern bias in Europe as regards enchytraeid community ecology, particularly in urban settings. We approached the enchytraeid assemblages of urban holm oak stands in Naples and Siena adopting a high intensity sampling that, for the first time in the Mediterranean climate zone, would ensure that the data collected be representative of the target populations. Structural parameters (diversity and evenness, biomass, size classes, aggregation) were compared across different spatial (regional, urban district, within habitat) and temporal scales (season and year). Species richness was found to change significantly only at regional scale; background data suggest that this may depend on the higher environmental heterogeneity occurring at Naples. Differences in size class structure were significant only on a seasonal scale and within either city separately. With one exception (Fridericia bulbosa s.s.), the patterns of spatial aggregation of the common species were fairly robust and the total range of patchiness was consistent with previous studies, despite the different sampling methodologies. The size of the sampling unit, the number of replicates per plot and the number of plots proposed in this study appear suitable to obviate the difficulties of evaluating Mediterranean enchytraeid communities.

IRIDE:Interdisciplinary research infrastructure based on dual electron linacs and lasers

This paper describes the scientific aims and potentials as well as the preliminary technical design of IRIDE, an innovative tool for multi-disciplinary investigations in a wide field of scientific, technological and industrial applications. IRIDE will be a high intensity "particles factory", based on a combination of high duty cycle radio-frequency superconducting electron linacs and of high energy lasers. Conceived to provide unique research possibilities for particle physics, for condensed matter physics, chemistry and material science, for structural biology and industrial applications, IRIDE will open completely new research possibilities and advance our knowledge in many branches of science and technology. IRIDE is also supposed to be realized in subsequent stages of development depending on the assigned priorities. © 2013 Elsevier B.V.

Fast-electron refluxing effects on anisotropic hard-x-ray emission from intense laser-plasma interactions

Fast-electron generation and dynamics, including electron refluxing, is at the core of understanding high-intensity laser-plasma interactions. This field is itself of strong relevance to fast ignition fusion and the development of new short-pulse, intense, x-ray, gamma-ray, and particle sources. In this paper, we describe experiments that explicitly link fast-electron refluxing and anisotropy in hard-x-ray emission. We find the anisotropy in x-ray emission to be strongly correlated to the suppression of refluxing. In contrast to some previous work, the peak of emission is directly along the rear normal to the target rather than along either the incident laser direction or the specular reflection direction.

Testing numerical implementations of strong-field electrodynamics

We test current numerical implementations of laser-matter interactions by comparison with exact analytical results. Focusing on photon emission processes, it is found that the numerics accurately reproduce analytical emission spectra in all considered regimes, except for the harmonic structures often singled out as the most significant high-intensity (multiphoton) effects. We find that this discrepancy originates in the use of the locally constant field approximation.

Harmonic Generation from Relativistic Plasma Surfaces in Ultrasteep Plasma Density Gradients

Harmonic generation in the limit of ultrasteep density gradients is studied experimentally. Observations reveal that, while the efficient generation of high order harmonics from relativistic surfaces requires steep plasma density scale lengths (L-p/lambda <1), the absolute efficiency of the harmonics declines for the steepest plasma density scale length L-p -> 0, thus demonstrating that near-steplike density gradients can be achieved for interactions using high-contrast high-intensity laser pulses. Absolute photon yields are obtained using a calibrated detection system. The efficiency of harmonics reflected from the laser driven plasma surface via the relativistic oscillating mirror was estimated to be in the range of 10(-4)-10(-6) of the laser pulse energy for photon energies ranging from 20-40 eV, with the best results being obtained for an intermediate density scale length.

Evidence of locally enhanced target heating due to instabilities of counter-streaming fast electron beams

The high-current fast electron beams generated in high-intensity laser-solid interactions require the onset of a balancing return current in order to propagate in the target material. Such a system of counter-streaming electron currents is unstable to a variety of instabilities such as the current-filamentation instability and the two-stream instability. An experimental study aimed at investigating the role of instabilities in a system of symmetrical counter-propagating fast electron beams is presented here for the first time. The fast electron beams are generated by double-sided laser-irradiation of a layered target foil at laser intensities above 10(19) W/cm(2). High-resolution X-ray spectroscopy of the emission from the central Ti layer shows that locally enhanced energy deposition is indeed achieved in the case of counter-propagating fast electron beams

X-ray Polarization Measurements of Dense Plasmas Heated by Fast Electrons

The detailed knowledge of fast electron energy transport following interaction with high-intensity, ultra-short laser pulses is a key area for secondary source generation for ELI. We demonstrate polarization spectroscopy at laser intensities up to 10(21) Wcm(-2). This is significant as it suggests that in situ emission spectroscopy may be used as an effective probe of fast electron velocity distributions in regimes relevant to electron transport in solid targets. Ly-alpha doublet emission of nickel (Z = 28) and sulphur (Z = 16) is observed to measure the degree of polarization from the Ly-alpha(1) emission. Ly-alpha(2) emission is unpolarized, and as such acts as a calibration source between spectrometers. The measured ratio of the X-ray sigma- and pi-polarization allows the possibility to infer the velocity distribution function of the fast electron beam.

X-ray Polarization Spectroscopy from Ultra-Intense Interactions

Detailed knowledge of fast electron energy transport following the interaction of ultrashort intense laser pulses is a key subject for fast ignition. This is a problem relevant to many areas of laser-plasma physics with particular importance to fast ignition and X-ray secondary source development, necessary for the development of large-scale facilities such as HiPER and ELI. Operating two orthogonal crystal spectrometers set at Bragg angles close to 45 degrees determines the X-ray s- and p-polarization ratio. From this ratio, it is possible to infer the velocity distribution function of the fast electron beam within the dense plasma. We report on results of polarization measurements at high density for sulphur and nickel buried layer targets in the high intensity range of 10(19) - 10(21) Wcm(-2). We observe at 45 degrees the Ly-alpha doublet using two sets of orthogonal highly-orientated pyrolytic graphite (HOPG) crystals set in 1(st) order for sulphur and 3(rd) order for nickel.

Monitoring of saliva pH using miniaturized sensing tools as an indicator of oral health

The monitoring of oral disease is important, not alone for oral health, but for the detection and prevention of
systemic disease. The link between oral health and systemic disease is the focus of many studies, with
indications emerging of a causal link [1]. For disease diagnostics, blood has typically been the fluid of choice
for analysis, the retrieval of which is invasive and therefore unsuitable for wearable technology. Analysis of
saliva, however, is less invasive than that of blood, requires little or no pre-treatment and is abundantly
available. A strong correlation has been found between the analytes of blood and saliva [2] with saliva
containing biomarkers for diseases such as diabetes, oral cancer and cardiovascular disease. The development of
an implantable multi-parametric wireless sensor, to monitor both salivary analytes and changes in gingival
temperature, is the aim of this research project.
The aim of our current study is to detect changes in salivary pH, using a gold electrode with a pHsensitive
iridium oxide layer, and an Ion Sensitive Field Effect Transistor probe. Characterisation studies were
carried out in artificial saliva (AS). A salivary pH of between 4.5pH-7.5pH [3], and gingival temperature
between 35°C-38°C [4], were identified as the target range of interest for the human oral environment. Sensor
measurements were recorded in solutions of varying pH and temperature. An ISFET probe was then implanted
into a prototype denture and characterised in AS. This study demonstrates the suitability of ISFET and gold
electrode pH sensors for incorporation into implantable oral sensors.
[1] G. Taylor and W. Borgnakke, “Periodontal disease: associations with diabetes, glycemic control and
complications,” Oral Dis., vol. 14, no. 3, pp. 191–203, Apr. 2008.
[2] E. Tékus, M. Kaj, E. Szabó, N. L. Szénási, I. Kerepesi, M. Figler, R. Gábriel, and M. Wilhelm,
“Comparison of blood and saliva lactate level after maximum intensity exercise,” Acta Biol. Hung., vol. 63
Suppl 1, pp. 89–98, 2012.
[3] S. Naveen, M. L. Asha, G. Shubha, A. Bajoria, and A. Jose, “Salivary Flow Rate, pH and Buffering
Capacity in Pregnant and Non Pregnant Women - A Comparative Study,” JMED Res., pp. 1–8, Feb. 2014.
[4] A. F. Holthuis and F. S. Chebib, “Observations on temperature and temperature patterns of the gingiva. I.
The effect of arch, region and health,” J. Periodontol., vol. 54, no. 10, pp. 624–628, Oct. 1983

Plasma levels of intermedin (adrenomedullin-2) in healthy human volunteers and patients with heart failure

Intermedin/adrenomedullin-2 (IMD) is a member of the adrenomedullin/CGRP peptide family. Less is known about the distribution of IMD than for other family members within the mammalian cardiovascular system, particularly in humans. The aim was to evaluate plasma IMD levels in healthy subjects and patients with chronic heart failure. IMD and its precursor fragments, preproIMD25–56 and preproIMD57–92, were measured by radioimmunoassay in 75 healthy subjects and levels of IMD were also compared to those of adrenomedullin (AM) and mid-region proadrenomedullin45–92 (MRproAM45–92) in 19 patients with systolic heart failure (LVEF < 45%). In healthy subjects, plasma levels (mean + SE) of IMD (6.3 + 0.6 pg ml−1) were lower than, but correlated with those of AM (25.8 + 1.8 pg ml−1; r = 0.49, p < 0.001). Plasma preproIMD25–56 (39.6 + 3.1 pg ml−1), preproIMD57–92 (25.9 + 3.8 pg ml−1) and MRproAM45–92 (200.2 + 6.7 pg ml−1) were greater than their respective bioactive peptides. IMD levels correlated positively with BMI but not age, and were elevated in heart failure (9.8 + 1.3 pg ml−1, p < 0.05), similarly to MRproAM45–92 (329.5 + 41.9 pg ml−1, p < 0.001) and AM (56.8 + 10.9 pg ml−1, p < 0.01). IMD levels were greater in heart failure patients with concomitant renal impairment (11.3 + 1.8 pg ml−1) than those without (6.5 + 1.0 pg ml−1; p < 0.05). IMD and AM were greater in patients receiving submaximal compared with maximal heart failure drug therapy and were decreased after 6 months of cardiac resynchronization therapy. In conclusion, IMD is present in the plasma of healthy subjects less abundantly than AM, but is similarly correlated weakly with BMI. IMD levels are elevated in heart failure, especially with concomitant renal impairment, and tend to be reduced by high intensity drug or pacing therapy.

Dynamic control of laser driven proton beams by exploiting self-generated, ultrashort electromagnetic pulses

As part of the ultrafast charge dynamics initiated by high intensity laser irradiations of solid targets,high amplitude EM pulses propagate away from the interaction point and are transported along anystalks and wires attached to the target. The propagation of these high amplitude pulses along a thinwire connected to a laser irradiated target was diagnosed via the proton radiography technique,measuring a pulse duration of 20 ps and a pulse velocity close to the speed of light. The strongelectric field associated with the EM pulse can be exploited for controlling dynamically the protonbeams produced from a laser-driven source. Chromatic divergence control of broadband laser drivenprotons (upto 75% reduction in divergence of >5 MeV protons) was obtained by winding the supportingwire around the proton beam axis to create a helical coil structure. In addition to providingfocussing and energy selection, the technique has the potential to post-accelerate the transiting protonsby the longitudinal component of the curved electric field lines produced by the helical coil lens.