Search

Boreal forests hold 32% of the world’s terrestrial organic matter and are continually disturbed by biotic and abiotic events. These disturbances are especially important since they facilitate the redistribution of nutrients within and between ecosystems, which can alter resource use and productivity. Yet how various types of disturbances, both individually and in combination, impact the overall resource balance of northern forests remains poorly understood. This thesis aims to advance our understanding of forest disturbances as drivers of forest resource balances, primarily through shifts in carbon, to better facilitate management of forests under climate change. Chapter 1 reviews current knowledge on forest disturbances and cross- ecosystem linkages. It also provides a summary of current gaps in our understanding of disturbances as drivers of forest function and possible downstream effects. Chapter 2 explores how disturbance history influences long-term carbon balance in boreal forests. Theory predicts that disturbances will increase with climate change but how the order and timing of multiple disturbance events will impact ecosystem function remains unresolved. Chapter 3 extends our understanding of forest carbon balance by asking how different disturbance types change the phenology and surface reflectance of boreal forests. Understanding how single disturbance events change growing season length and radiative forcing of forests can help predict potential feedbacks of forest health on climate warming. Chapter 4 tests how outbreaks of defoliating insects alter biogeochemical cycling from land to receiving waters through the consumption of foliage and subsequent release of nutrient-rich waste. Forests typically provide a pulse of nutrients to nearby waters in autumn when leaves are shed but insects disrupt this pattern by changing the timing, quantity, and quality of resource transfers. Chapter 5 traces terrestrial nutrients within lakes and asks if they can promote productivity in zooplankton communities. Finally, Chapter 6 discusses the main findings of the thesis and ends with possible directions for future research.

Magnetic resonance imaging, MRI, relying on (19)F nuclei has attracted much attention, because the isotopes exhibit a high gyromagnetic ratio (comparable to that of protons) and have 100% natural abundance. Furthermore, due to the very low traces of intrinsic fluorine in biological tissues, fluorine labeling allows easy visualization in vivo using (19)F-based MRI. However, one of the drawbacks of the available fluorine tracers is their very limited solubility in water. Here, we detail the design and preparation of a set of water-compatible fluorine-rich polymers as contrast agents that can enhance the effectiveness of (19)F-based MRI. The agents are synthesized using the nucleophilic addition reaction between poly(isobutylene-alt-maleic anhydride) copolymer and a mixture of amine-appended fluorine groups and polyethylene glycol (PEG) blocks. This allows control over the polymer architecture and stoichiometry, resulting in good affinity to water solutions. We further investigate the effects of introducing additional segmental mobility to the fluorine moieties in the polymer, by inserting a PEG linker between the moieties and the polymer backbone. We find that controlling the polymer stoichiometry and introducing additional segmental mobility enhance the NMR signals and narrow the peak profile. In particular, we assess the impact of the PEG linker on T(2)* and T(1) relaxation times, using a series of gradient-recalled echo images with varying echo times, TE, or recovery time, TR, respectively. We find that for equivalent concentrations, the PEG linker greatly increases T(2)*, while maintaining high T(1) values, as compared to polymers without this linker. Phantom images collected from these compounds show bright signals over a background with high intensities.

As the solar wind encounters a comet, ionized gas released from the nucleus propagates away from the Sun with the wind, forming the ion tail of the comet that can stretch for multiple astronomical units. The transport of cometary material antisunward of the comet provides opportunities to measure the cometary composition and plasma interactions at a significant distance from a comet’s nucleus. Serendipitous crossings by spacecraft of comets’ ion tails is a surprisingly commonplace occurrence, but can go unnoticed, as any measured plasma fluctuations can be small. Using the measured flow of the solar wind at the spacecraft, we can estimate the motion of the solar plasma upstream of the spacecraft, and compare this trajectory with the locations of known comets. This method can uncover previously unnoticed ion tail encounters and predict future encounters. In December 2021, while comet C/2021 A1 (Leonard) traversed the ecliptic plane, sunward of the spacecraft Solar Orbiter, the spacecraft was immersed in the comet’s ion tail. This encounter was predicted using a range of estimated solar wind velocities to estimate the motion of solar wind plasma to the spacecraft. A wealth of data was collected during the encounter, including results from multiple instruments that support the prediction. We present data returned from the SWA and magnetometer instruments, providing information on the structure of the induced magnetotail. Additionally, images of comet Leonard’s ion tail from other spacecraft during the encounter provide a uniquely complete picture of the tail crossing. Fig: Orbital configuration of comet Leonard and Solar Orbiter on 18th December 2021, during which Solar Orbiter was immersed in the ion tail of comet Leonard.

The use of digital templating for Total Hip Arthroplasty (THA) is now the standard approach for pre-operative planning. Digital templating holds potential to reduce operative time and post-op complications however, this often relies on imprecise assumptions. The relationship between the X-ray source, subject and detector alters the perceived magnification. We therefore determine if Body Mass Index (BMI) is positively correlated with true magnification and if a predictive model based these parameters exists. A single surgeon series (n=107) was included in this study. Two independent observers assessed both pre- and post-operative AP pelvis radiographs using TraumaCad™. Post-operative radiographs were assessed to calculate the true magnification by calibrating from a known femoral head prosthesis size. Finally, a scatter plot with regression was used to determine if a predictive model of magnification existed using the Body Mass Index. The mean pre-operative magnification using a scaling marker was 124.2 ± 8.90%. The mean post-operative magnification using a known femoral head prosthesis size (true magnification) was 123.7 ± 3.98%. Significant variability exists in pre-operative marker data. Regression modelling showed no significant correlation between BMI and true magnification (post-op magnification). This study’s suggests that the precision and reliability of the radiographic marker in daily practice is poor. Regression modelling showed no significant correlation between BMI and the true magnification factor. Therefore, a pre-op predictive model cannot be reliably used. The data from this study suggest that a fixed magnification factor of 124% remains the most reliable and accurate method.

Previous examination of fully-convective M-dwarf stars highlighted unexplained enhanced rates of nanoflare activity. A potential explanation was linked to the helical turbulence dynamo which operates in fully convective stars. However, recent studies have found this helical dynamo does not appear significantly different to the Solar dynamo. The specific role the convective boundary plays on observed nanoflare rates, until now, was not known. Here we find evidence that fully convective M2.5V (and later) stars display greatly enhanced nanoflare rates compared with their pre-convective boundary counterparts. Importantly, the rate of nanoflare activity increases with increasing spectral sub-type, with nanoflares exhibiting greatly enhanced flaring rates via Sweet-Parker reconnection. This occurs more favourably at increased plasma resistivities experienced in these later MV stars, suggesting a direct interplay between the rate of nanoflare occurrence and the intrinsic plasma parameters. As such, nanoflare behaviour is likely to be unrelated to the behaviour of the local dynamo.

Vessels engaged in the evasion of maritime sanctions are predominantly flagged by open registries: registries that impose little to no nationality requirements on vessel owners and operators. This paper investigates the causes of this phenomenon, arguing that open registries generally lack adequate measures for detecting sanctions evasion in their fleets and that they are targeted for flagging services by sanctions evaders. At the root of this vulnerability to flagging sanctions evaders is the for-profit nature of the open registry system which encourages registries to jettison regulation and oversight to increase their marketability in the competitive industry of international flagging.

BackgroundThe process of obtaining informed consent is an important and complex pursuit, especially within a paediatric setting. Medical governing bodies have stated that the role of the trainee surgeon must be explained to patients and their families during the consent process. Despite this, attitudes and practices of surgeons and their trainees regarding disclosure of the trainee’s participation during the consent process has not been reported in the paediatric setting.MethodsNineteen face-to-face interviews were conducted with surgical trainees and staff surgeons at a tertiary-level paediatric hospital in Toronto, Canada. These were transcribed and subsequently thematically coded by three reviewers.ResultsFive main themes were identified from the interviews. (1) Surgeons do not consistently disclose the role of surgical trainees to parents. (2) Surgical trainees are purposefully vague in disclosing their role during the consent discussion without being misleading. (3) Surgeons and surgical trainees believe parents do not fully understand the specific role of surgical trainees. (4) Graduated responsibility is an important aspect of training surgeons. (5) Surgeons feel a responsibility towards both their patients and their trainees. Surgeons do not explicitly inform patients about trainees, believing there is a lack of understanding of the training process. Trainees believe families likely underestimate their role and keep information purposely vague to reduce anxiety.ConclusionThe majority of surgeons and surgical trainees do not voluntarily disclose the degree of trainee participation in surgery during the informed consent discussion with parents. An open and honest discussion should occur, allowing for parents to make an informed decision regarding their child’s care. Further patient education regarding trainees’ roles would help develop a more thorough and patient-centred informed consent process.

A 22 year old man presented to the department of oral and maxillofacial surgery with a five day history of sore throat, pain on swallowing, and low grade fever. He was previously fit and well with no medical history of note. His lower wisdom teeth had been extracted seven days before presentation. He was a non-smoker and non-drinker. On examination, he looked unwell with tachycardia (120 beats/min) and a temperature of 37.2oC. He was normotensive and mildly tachypnoeic (22 breaths/min). Oropharyngeal examination was difficult owing to marked trismus, but a raised floor of the mouth was noted. He had a tender swelling in his upper neck extending to bilateral submandibular regions and a “hot potato” voice. Initial investigations showed a raised white cell count of 29.9×109/L (reference range 4.5-11) and a C reactive protein (CRP) of 4343 nmol/L (0.76-28.5). Urgent contrast enhanced computed tomography of his head and neck was performed (fig 1⇓). ### 1. What is the likely diagnosis? #### Short answer Signs and symptoms suggest a fulminating infection of the neck. Elevation of the floor of the mouth and hot potato speech suggest involvement of deeper fascial spaces. The diagnosis is Ludwig’s angina. #### Discussion The signs and symptoms are typical of Ludwig’s angina and impending airway obstruction. This condition was first described by Wilhelm Fredrick von Ludwig in 1836 as a rapidly evolving cellulitis around the neck originating from submandibular regions.1 It is a rare surgical emergency—among 365 cases of deep neck infections, the incidence of Ludwig’s angina was 4.1%.2 The incidence was higher in another series, at 8% among 112 cases of deep space neck infections.3 A …

OPTRA has developed a two-band midwave infrared (MWIR) scene projector based on digital micromirror device (DMD) technology; the projector is intended for training various IR tracking systems that exploit the relative intensities of two separate MWIR spectral bands. Next generation tracking systems have increasing dynamic range requirements which current DMD-based projector test equipment is not capable of meeting. While sufficient grayscale digitization can be achieved with current drive electronics, commensurate contrast is not currently available. It is towards this opportunity that OPTRA has initiated a dynamic range design improvement effort. In this paper we present our work towards the measurement and analysis of contrast limiting factors including substrate scattering, diffraction, and flat state emissivity. We summarize the results of an analytical model which indicates the largest contributions to background energy in the off state. We present the methodology and results from a series of breadboard tests designed to characterize these contributions. Finally, we suggest solutions to counter these contributions.