Symmetry of two terminal, non-linear electric conduction

The well-established symmetry relations for linear transport phenomena can not, in general, be applied in the non-linear regime. Here we propose a set of symmetry relations with respect to bias voltage and magnetic field for the non-linear conductance of two-terminal electric conductors. We experimentally confirm these relations using phase-coherent, semiconductor quantum dots.Comment: 4 pages, 4 figure

Aluminium and base cation chemistry in dynamic acidification models – need for a reappraisal?

Long-term simulations of the water composition in acid forest soils require that accurate descriptions of aluminium and base cation chemistry are used. Both weathering rates and soil nutrient availability depend on the concentrations of Al3+, of H+, and of base cations (Ca2+, Mg2+, Na+, and K+) . Assessments of the acidification status and base cation availability will depend on the model being used. Here we review in what ways different dynamic soil chemistry models describe the processes governing aluminium and base cation concentrations in the soil water. Furthermore, scenario simulations with the HD-MINTEQ model are used to illustrate the difference between model approaches. The results show that all investigated models provide the same type of response to changes in input water chemistry. Still, for base cations we show that the differences in the magnitude of the response may be considerable depending on whether a cation-exchange equation (Gaines–Thomas, Gapon) or an organic complexation model is used. The former approach, which is used in many currently used models (e.g. MAGIC, ForSAFE), causes stronger pH buffering over a relatively narrow pH range, as compared to state-of-the-art models relying on more advanced descriptions in which organic complexation is important (CHUM, HD-MINTEQ). As for aluminium, a fixed gibbsite constant, as used in MAGIC, SMART/VSD, and ForSAFE, leads to slightly more pH buffering than in the more advanced models that consider both organic complexation and Al(OH)3(s) precipitation, but in this case the effect is small. We conclude that the descriptions of acid–base chemistry and base cation binding in models such as MAGIC, SMART/VSD, and ForSAFE are only likely to work satisfactorily in a narrow pH range. If the pH varies greatly over time, the use of modern organic complexation models is preferred over cation-exchange equations.</p

Assessing the impact of acid rain and forest harvest intensity with the HD-MINTEQ model – soil chemistry of three Swedish conifer sites from 1880 to 2080

Forest soils are susceptible to anthropogenic acidification. In the past, acid rain was a major contributor to soil acidification, but, now that atmospheric levels of S have dramatically declined, concern has shifted towards biomass-induced acidification, i.e. decreasing soil solution pH due to tree growth and harvesting events that permanently remove base cations (BCs) from forest stands. We use a novel dynamic model, HD-MINTEQ (Husby Dynamic MINTEQ), to investigate possible long-term impacts of two theoretical future harvesting scenarios in the year 2020, a conventional harvest (CH, which removes stems only), and a whole-tree harvest (WTH, which removes 100&thinsp;% of the above-ground biomass except for stumps) on soil chemistry and weathering rates at three different Swedish forest sites (Aneboda, Gårdsjön, and Kindla). Furthermore, acidification following the harvesting events is compared to the historical acidification that took place during the 20th century due to acid rain. Our results show that historical acidification due to acid rain had a larger impact on pore water chemistry and mineral weathering than tree growth and harvesting, at least if nitrification remained at a low level. However, compared to a no-harvest baseline, WTH and CH significantly impacted soil chemistry. Directly after a harvesting event (CH or WTH), the soil solution pH sharply increased for 5 to 10 years before slowly declining over the remainder of the simulation (until year 2080). WTH acidified soils slightly more than CH, but in certain soil horizons there was practically no difference by the year 2080. Even though the pH in the WTH and CH scenario decreased with time as compared to the no-harvest scenario (NH), they did not drop to the levels observed around the peak of historic acidification (1980–1990), indicating that the pH decrease due to tree growth and harvesting would be less impactful than that of historic atmospheric acidification. Weathering rates differed across locations and horizons in response to historic acidification. In general, the predicted changes in weathering rates were very small, which can be explained by the net effect of decreased pH and increased Al3+, which affected the weathering rate in opposite ways. Similarly, weathering rates after the harvesting scenarios in 2020 remained largely unchanged according to the model.</p

Remote Detection of Radioactive Material using High-Power Pulsed Electromagnetic Radiation

Remote detection of radioactive materials is impossible when the measurement location is far from the radioactive source such that the leakage of high-energy photons or electrons from the source cannot be measured. Current technologies are less effective in this respect because they only allow the detection at distances to which the high-energy photons or electrons can reach the detector. Here we demonstrate an experimental method for remote detection of radioactive materials by inducing plasma breakdown with the high-power pulsed electromagnetic waves. Measurements of the plasma formation time and its dispersion lead to enhanced detection sensitivity compared to the theoretically predicted one based only on the plasma on and off phenomena. We show that lower power of the incident electromagnetic wave is sufficient for plasma breakdown in atmospheric-pressure air and the elimination of the statistical distribution is possible in the presence of radioactive material.ope

Clinical and radiological evaluation of Trabecular Metal and the Smith–Robinson technique in anterior cervical fusion for degenerative disease: a prospective, randomized, controlled study with 2-year follow-up

A prospective, randomized, controlled study was carried out to compare the radiological and clinical outcomes after anterior cervical decompression and fusion (ACDF) with Trabecular Metal™ (TM) to the traditional Smith–Robinson (SR) procedure with autograft. The clinical results of cervical fusion with autograft from the iliac crest are typically satisfactory, but implications from the donor site are frequently reported. Alternative materials for cervical body interfusion have shown lower fusion rates. Trabecular Metal is a porous tantalum biomaterial with structure and mechanical properties similar to that of trabecular bone and with proven osteoconductivity. As much as 80 consecutive patients planned for ACDF were randomized for fusion with either TM or tricortical autograft from the iliac crest (SR) after discectomy and decompression. Digitized plain radiographic images of 78 (98%) patients were obtained preoperatively and at 2-year follow-up and were subsequently evaluated by two senior radiologists. Fusion/non-fusion was classified by visual evaluation of the A–P and lateral views in forced flexion/extension of the cervical spine and by measuring the mobility between the fused vertebrae. MRI of 20 TM cases at 2 years was successfully used to assess the decompression of the neural structures, but was not helpful in determining fusion/non-fusion. Pain intensity in the neck, arms and pelvis/hip were rated by patients on a visual analog scale (VAS) and neck function was rated using the Neck Disability Index (NDI) the day before surgery and 4, 12 and 24 months postoperatively. Follow-ups at 12 and 24 months were performed by an unbiased observer, when patients also assessed their global outcome. Fusion rate in the SR group was 92%, and in the TM group 69% (P < 0.05). The accuracy of the measurements was calculated to be 2.4°. Operating time was shorter for fusion with TM compared with autograft; mean times were 100 min (SD 18) and 123 min (SD 23), respectively (P = 0.001). The patients’ global assessments of their neck and arm symptoms 2 years postoperatively for the TM group were rated as 79% much better or better after fusion with TM and 75% using autograft. Pain scores and NDI scores were significantly improved in both groups when compared with baseline at all follow-ups, except for neck pain at 1 year for the TM group. There was no statistically significant difference in clinical outcomes between fusion techniques or between patients who appeared radiologically fused or non-fused. There was no difference in pelvic/hip pain between patients operated on with or without autograft. In our study, Trabecular Metal showed a lower fusion rate than the Smith–Robinson technique with autograft after single-level anterior cervical fusion without plating. There was no difference in clinical outcomes between the groups. The operative time was shorter with Trabecular Metal implants