Imaging and monitoring tree-induced subsidence using electrical resistivity imaging

Tree-induced subsidence is a natural ground movement phenomenon that arises when tree roots absorb water from clay-rich soils, causing them to shrink. Tree-induced subsidence is particularly problematic for buildings and structures in close proximity to deciduous trees where changes in seasonal climate can have a significant effect on the degree of relative surface movement. Unfortunately, there is a lack of in-depth understanding of tree-induced subsidence dynamics and limited access to affordable/reliable assessment technologies for the victims of such phenomena. This paper presents and discusses the use of 2D electrical resistivity imaging (ERI) as a tool for recognizing tree-related subsurface desiccation and its associated subsidence. The findings of a two year ERI study in a high-risk tree-induced subsidence environment are presented (mature Oak and Willow trees growing in expansive London Clays) where repeat (time-lapse) resistivity profiles are compared to conventional ground levelling and soil moisture content data. This study confirms that ERI is a valuable tool for the characterization of seasonally varying subsurface moisture distributions and that the technique is capable of defining the architecture and temporal-spatial variance of an active tree root system. Moreover, the method provides a critical insight into the visualization of tree-induced subsidence phenomena and reveals promising practical potential for use as a modern, affordable, non-invasive tree-induced subsidence assessment tool

Familiarisation to maximal recumbent eccentric cycling

BACKGROUND: Isokinetic eccentric cycling is increasingly being utilised to examine the effect of chronic eccentric muscle training however little is known about how individuals familiarise to such a unique training modality. OBJECTIVE: To examine longitudinal variation in power output and lower limb muscle activation during familiarisation to maximal recumbent isokinetic eccentric cycling. METHODS: Twelve male volunteers, unfamiliar with eccentric cycling, completed four trials, separated by 7-10 days, each comprising 6 × 10 s maximal isokinetic eccentric efforts between 20-120 rpm. Peak power and average power output (PO), and surface electromyography (sEMG) of the rectus femoris (RF), vastus lateralis (VL), biceps femoris (BF), and medial gastrocnemius (MG) were recorded throughout. Systematic error across repeated trials was assessed using one-way ANOVA, and random error quantified using coefficient of variation (CV, %). RESULTS: Average PO at 60 rpm and RF activation at 20 rpm increased from trial 1-2 (p < 0.05), with no other systematic error between trials at any cadence. Across all cadences, the CV for peak PO (∼ 13%), average PO (∼ 10%), VL activation (∼ 13%) and RF activation (∼ 19%) was moderate and plateaued after one familiarisation (i.e. T2-T3). However, for BF (∼ 24%) and MG (∼ 22%) activation reliability was generally poor. For the majority of variables the reliability was best at 60 rpm. CONCLUSIONS: Therefore, with one familiarisation, 60 rpm is recommended to achieve moderate between-session reliability in the measurement of power output and lower limb muscle activation during recumbent, eccentric cycling

Comparison of geophysical and botanical results in simulated clandestine graves in rural and tropical environments in Colombia, South America

In most Latin American countries there are significant numbers of both missing people and forced disappearances, ~84,000 alone in Colombia. Successful detection of buried human remains by forensic search teams can be difficult in varying terrain and climates. This paper reports on the geophysical and botanical monitoring of simulated clandestine graves in two different environments over 24 months to establish optimal detection methods and equipment configurations. Twelve clandestine burials were simulated at three different burial depths (0.5m, 0.8 m and 1.2 m) commonly encountered in Latin America. The simulated targets were three pig carcasses, three human skeletons, three graves with burnt human beheaded skeletons and finally three empty graves to act as control. Geophysical detection methods included ground penetrating radar, magnetic susceptibility, bulk ground conductivity and electrical resistivity. Geophysical results showed apparent electrical resistivity was optimal to detect targets (85% success) in semi-rural areas and GPR was optimal to detect targets (92%) in tropical rainforest areas, followed by magnetic susceptibility and bulk ground conductivity. Botanical results evidenced variations in both study sites which should be noted by forensic search investigators, with rapid growth of Raphanus in the tropical rainforest graves and Malvaceae and Petiveria in the rural study site respectively. This paper shows the importance of conducting long-term controlled studies to assist forensic search teams with expected results and optimum equipment configuration(s)

Torque, power and muscle activation of eccentric and concentric isokinetic cycling

This study aimed to establish the effect of cycling mode and cadence on torque, external power output, and lower limb muscle activation during maximal, recumbent, isokinetic cycling. After familiarisation, twelve healthy males completed 6 × 10 s of maximal eccentric (ECC) and concentric (CON) cycling at 20, 40, 60, 80, 100, and 120 rpm with five minutes recovery. Vastus lateralis, medial gastrocnemius, rectus femoris, and biceps femoris surface electromyography was recorded throughout. As cadence increased, peak torque linearly decreased during ECC (350-248 N·m) and CON (239-117 N·m) and peak power increased in a parabolic manner. Crank angle at peak torque increased with cadence in CON (+13°) and decreased in ECC (-9.0°). At all cadences, peak torque (mean +129 N·m, range 111-143 N·m), and power (mean +871 W, range 181-1406 W), were greater during ECC compared to CON. For all recorded muscles the crank angle at peak muscle activation was greater during ECC compared to CON. This difference increased with cadence in all muscles except the vastus lateralis. Additionally, peak vastus laterallis and biceps femoris activation was greater during CON compared to ECC. Eccentric cycling offers a greater mechanical stimulus compared to concentric cycling but the effect of cadence is similar between modalities. Markers of technique (muscle activation, crank angle at peak activation and torque) were different between eccentric and concentric cycling and respond differently to changes in cadence. Such data should be considered when comparing between, and selecting cadences for, recumbent, isokinetic, eccentric and concentric cycling

Cooperative Lewis pairs based on late transition metals: activation of small molecules by platinum(0) and B(C6F5)3

A Lewis basic platinum(0)–CO complex supported by a diphosphine ligand and B(C6F5)3 act cooperatively, in a manner reminiscent of a frustrated Lewis pair, to activate small molecules such as hydrogen, CO2, and ethene. This cooperative Lewis pair facilitates the coupling of CO and ethene in a new way

Long-term Geophysical Monitoring of Simulated Clandestine Graves using Electrical and Ground Penetrating Radar Methods: 4–6 Years After Burial

This ongoing monitoring study provides forensic search teams with systematic geophysical data over simulated clandestine graves for comparison to active cases. Simulated “wrapped,”“naked,” and “control” burials were created. Multiple geophysical surveys were collected over 6 years, here showing data from 4 to 6 years after burial. Electrical resistivity (twin electrode and ERI), multifrequency GPR, grave and background soil water were collected. Resistivity surveys revealed that the naked burial had low-resistivity anomalies up to year four but then difficult to image, whereas the wrapped burial had consistent large high-resistivity anomalies. GPR 110- to 900-MHz frequency surveys showed that the wrapped burial could be detected throughout, but the naked burial was either not detectable or poorly resolved. 225-MHz frequency GPR data were optimal. Soil water analyses showed decreasing (years 4 to 5) to background (year 6) conductivity values. Results suggest both resistivity and GPR surveying if burial style unknown, with winter to spring surveys optimal and increasingly important as time increases

The use of geoscience methods for aquatic forensic searches

There have been few publications on the forensic search of water and fewer still on the use of geoforensic techniques when exploring aqueous environments. Here we consider what the nature of the aqueous environment is, what the forensic target(s) may be, update the geoforensic search assets we may use in light of these, and provide a search strategy that includes multiple exploration assets. Some of the good practice involved in terrestrial searches has not been applied to water to-date, water being seen as homogenous and without the complexity of solid ground: this is incorrect and a full desktop study prior to searching, with prioritized areas, is recommended. Much experimental work on the decay of human remains is focused on terrestrial surface deposition or burial, with less known about the nature of this target in water, something which is expanded upon here, in order to deploy the most appropriate geoforensic method in water-based detection. We include case studies where detecting other forensic targets have been searched for; from metal (guns, knives) to those of a nonmetallic nature, such as submerged barrels/packages of explosives, drugs, contraband and items that cause environmental pollution. A combination of the consideration of the environment, the target(s), and both modern and traditional search devices, leads to a preliminary aqueous search strategy for forensic targets. With further experimental research and criminal/humanitarian casework, this strategy will continue to evolve and improve our detection of forensic targets

Semblance analysis to assess GPR data from a five-year forensic study of simulated clandestine graves

Ground penetrating radar (GPR) surveys have proven useful for locating clandestine graves in a number of forensic searches. There has been extensive research into the geophysical monitoring of simulated clandestine graves in different burial scenarios and ground conditions. Whilst these studies have been used to suggest optimum dominant radar frequencies, the data themselves have not been quantitatively analysed to-date. This study uses a common-offset configuration of semblance analysis, both to characterise velocity trends from GPR diffraction hyperbolae and, since the magnitude of a semblance response is proportional to signal-to-noise ratio, to quantify the strength of a forensic GPR response. 2D GPR profiles were acquired over a simulated clandestine burial, with a wrapped-pig cadaver monitored at three-month intervals between 2008 and 2013 with GPR antennas of three different centre-frequencies (110, 225 and 450 MHz). The GPR response to the cadaver was a strong diffraction hyperbola. Results show, in contrast to resistivity surveys, that semblance analysis show little sensitivity to changes attributable to decomposition, and only a subtle influence of seasonality: velocity increases (0.01–0.02 m/ns) were observed in summer, associated with a decrease (5–10%) in peak semblance magnitude, SM, and potentially in the reflectivity of the cadaver. The lowest-frequency antennas consistently gave the highest signal-to-noise ratio although the grave was nonetheless detectable by all frequencies trialled. These observations suggest that forensic GPR surveys could be undertaken with little seasonal hindrance. Whilst GPR analysis cannot currently provide a quantitative diagnostic proxy for time-since-burial, the consistency of responses suggests that graves will remain detectable beyond the five years shown here

Geophysical and botanical monitoring of simulated graves in a tropical rainforest, Colombia, South America

In most Latin American countries there are significant numbers of missing people and forced disappearances, currently ~74,000 only in Colombia. Successful detection of shallow buried human remains by forensic search teams is currently difficult in varying terrain and climates. Within this research we built four simulated clandestine burial styles in tropical rainforests, as this is a common scenario and depositional environment encountered in Latin America, to gain knowledge of optimum forensic geophysics detection techniques. The results of geophysically monitoring these burials using ground penetrating radar, magnetic susceptibility, bulk ground conductivity and electrical resistivity are presented from one to forty three weeks post-burial. Radar survey results with both the 250 MHz and 500 MHz frequency antennae showed good detection of modern simulated burials on 2D profiles and horizontal time slices but poor detection on the other simulated graves. Magnetic susceptibility, bulk ground conductivity and electrical resistivity results were generally poor at detecting the simulated targets. Observations of botanical variations on the test site show rapid re-growth of Malvaceae and Petiveria alliacea vegetation over all burials that are common in these forests, which can make detection more difficult