Heterogeneous Ice Nucleation by Soufriere Hills Volcanic Ash Immersed in Water Droplets.

Fine particles of ash emitted during volcanic eruptions may sporadically influence cloud properties on a regional or global scale as well as influencing the dynamics of volcanic clouds and the subsequent dispersion of volcanic aerosol and gases. It has been shown that volcanic ash can trigger ice nucleation, but ash from relatively few volcanoes has been studied for its ice nucleating ability. In this study we quantify the efficiency with which ash from the Soufriere Hills volcano on Montserrat nucleates ice when immersed in supercooled water droplets. Using an ash sample from the 11th February 2010 eruption, we report ice nucleating efficiencies from 246 to 265 K. This wide range of temperatures was achieved using two separate droplet freezing instruments, one employing nanolitre droplets, the other using microlitre droplets. Soufriere Hills volcanic ash was significantly more efficient than all other ash samples that have been previously examined. At present the reasons for these differences are not understood, but may be related to mineralogy, amorphous content and surface chemistry.

The relevance of nanoscale biological fragments for ice nucleation in clouds.

Most studies of the role of biological entities as atmospheric ice-nucleating particles have focused on relatively rare supermicron particles such as bacterial cells, fungal spores and pollen grains. However, it is not clear that there are sufficient numbers of these particles in the atmosphere to strongly influence clouds. Here we show that the ice-nucleating activity of a fungus from the ubiquitous genus Fusarium is related to the presence of nanometre-scale particles which are far more numerous, and therefore potentially far more important for cloud glaciation than whole intact spores or hyphae. In addition, we quantify the ice-nucleating activity of nano-ice nucleating particles (nano-INPs) washed off pollen and also show that nano-INPs are present in a soil sample. Based on these results, we suggest that there is a reservoir of biological nano-INPs present in the environment which may, for example, become aerosolised in association with fertile soil dust particles.

Adsorption and destruction of PCDD/Fs using surface-functionalized activated carbons.

Activated carbon adsorbs polychlorinated dibenzo-p-dioxins and -furans (PCDD/Fs) from gas streams but can simultaneously generate PCDD/Fs via de novo synthesis, increasing an already serious disposal problem for the spent sorbent. To increase activated carbon's PCDD/F sorption capacity and lifetime while reducing the impact of hazardous waste, it is beneficial to develop carbon-based sorbents that simultaneously destroy PCDD/Fs while adsorbing the toxic chemicals from gas streams. In this work, hydrogen-treated and surface-functionalized (i.e., oxygen, bromine, nitrogen, and sulfur) activated carbons are tested in a bench-scale reactor as adsorbents for PCDD/Fs. All tested carbons adsorb PCDD/F efficiently, with international toxic equivalent removal efficiencies exceeding 99% and mass removal efficiencies exceeding 98% for all but one tested material. Hydrogen-treated materials caused negligible destruction and possible generation of PCDD/Fs, with total mass balances between 100% and 107%. All tested surface-functionalized carbons, regardless of functionality, destroyed PCDD/Fs, with total mass balances between 73% and 96%. Free radicals on the carbon surface provided by different functional groups may contribute to PCDD/F destruction, as has been hypothesized in the literature. Surface-functionalized materials preferentially destroyed higher-order (more chlorine) congeners, supporting a dechlorination mechanism as opposed to oxidation. Carbons impregnated with sulfur are particularly effective at destroying PCDD/Fs, with destruction efficiency improving with increasing sulfur content to as high as 27%. This is relevant because sulfur-treated carbons are used for mercury adsorption, increasing the possibility of multi-pollutant control.

Ice nucleation by particles immersed in supercooled cloud droplets.

The formation of ice particles in the Earth's atmosphere strongly affects the properties of clouds and their impact on climate. Despite the importance of ice formation in determining the properties of clouds, the Intergovernmental Panel on Climate Change (IPCC, 2007) was unable to assess the impact of atmospheric ice formation in their most recent report because our basic knowledge is insufficient. Part of the problem is the paucity of quantitative information on the ability of various atmospheric aerosol species to initiate ice formation. Here we review and assess the existing quantitative knowledge of ice nucleation by particles immersed within supercooled water droplets. We introduce aerosol species which have been identified in the past as potentially important ice nuclei and address their ice-nucleating ability when immersed in a supercooled droplet. We focus on mineral dusts, biological species (pollen, bacteria, fungal spores and plankton), carbonaceous combustion products and volcanic ash. In order to make a quantitative comparison we first introduce several ways of describing ice nucleation and then summarise the existing information according to the time-independent (singular) approximation. Using this approximation in combination with typical atmospheric loadings, we estimate the importance of ice nucleation by different aerosol types. According to these estimates we find that ice nucleation below about -15 °C is dominated by soot and mineral dusts. Above this temperature the only materials known to nucleate ice are biological, with quantitative data for other materials absent from the literature. We conclude with a summary of the challenges our community faces.

Subdural hematomas in infants with benign enlargement of the subarachnoid spaces are not pathognomonic for child abuse.

BACKGROUND AND PURPOSE: Patients who have benign enlargement of the subarachnoid spaces (BESS) have long been suspected of having an increased propensity for subdural hematomas either spontaneously or as a result of accidental injury. Subdural hematomas in infants are often equated with nonaccidental trauma (NAT). A better understanding of the clinical and imaging characteristics of subdural hematomas that occur either spontaneously or as a result of accidental trauma may help distinguish this group of patients from those who suffer subdural hematomas as a result of NAT. The purpose of this study is to describe the clinical and imaging characteristics of subdural hematomas that occur either spontaneously or as a result of accidental injury in infants with BESS. METHODS: We conducted a retrospective review of all patients with BESS complicated by subdural hematomas evaluated at a single institution from 1998 to 2004. Data concerning the patient's clinical presentation, physical findings, imaging, and management are described. RESULTS: During the study period, 7 patients with BESS complicated by subdural hematoma were identified. Their mean age at identification of the subdural hematoma was 7.4 months of age. In 5 cases, there was no recognized trauma before identification of the subdural hematoma. In 3 cases, baseline CT or MR imaging was available, showing prominent subarachnoid spaces without any evidence of subdural hemorrhage. CONCLUSION: Although suspicious for NAT, subdural hematomas can occur in children either spontaneously or as a result of accidental trauma. Caution must be exercised when investigating for NAT based on the sole presence of subdural hematomas, especially in children who are otherwise well and who have BESS.

Use of prone ventilation in neurogenic pulmonary oedema.

We present a case of neurogenic pulmonary oedema (NPO) due to subarachnoid haemorrhage that resulted in hypoxia refractory to conventional mechanical ventilation. Prone positioning was employed, resulting in rapid and sustained improvement in oxygenation. We discuss the pathogenesis of NPO and the mechanism of action of prone ventilation. Prone ventilation may be of value in the management of NPO, both in treating life-threatening hypoxia and in optimizing neurological recovery. Further data are required on its effect on intracranial pressure after subarachnoid haemorrhage.

Predictors of poor outcome in patients with a spontaneous cerebellar hematoma.

BACKGROUND AND PURPOSE: The authors studied the clinical and neuroimaging features of cerebellar hematomas to predict poor outcome using comprehensive statistical models. METHODS: We retrospectively reviewed clinical and neuroimaging features in 94 patients with spontaneous cerebellar hematomas to identify predictive features for a poor neurologic outcome, defined as death or dismissal to long-term care facility. Data were analyzed using chi square and Fisher's exact test with calculation of odd's ratios together with 95% confidence intervals. RESULTS: Clinical and neuroradiologic predictors for a poor outcome at p < 0.05 were admission systolic blood pressure > 200 mm Hg, hematoma size > 3 cm, visible brain stem distortion, and acute hydrocephalus. Presenting findings predicting subsequent death at p < 0.05 were abnormal corneal and oculocephalic responses, Glasgow coma sum score less than 8, motor response less than localization to pain, acute hydrocephalus and intraventricular hemorrhage. CONCLUSION: A tree-based analysis model using binary recursive partitioning showed that cornea reflex, hydrocephalus, doll's eyes, age, and size were the most important discriminating factors. Absent corneal reflexes on admission highly predicts poor outcome (86 percent, confidence limits 67-96 percent). When a cornea reflex is present, acute hydrocephalus predicts poor outcome but only when doll's eyes are additionally absent.

Clinician's biases toward surgery in cerebellar hematomas: an analysis of decision-making in 94 patients.

BACKGROUND AND PURPOSE: No studies have examined clinical decision-making in cerebellar hemorrhages. Clinical and CT features may influence surgery in patients with a spontaneous cerebellar hematoma. One commonly accepted adage is to remove a clot when 3 cm or larger in axial diameter on presentation CT scan. It is possible that certain preferences impact on outcome. METHODS: We analyzed 94 patients with spontaneous cerebellar hematomas between the years of 1973-1993. Thirty-one patients underwent suboccipital craniectomy and clot removal with or without ventriculostomy. Deterioration denoted worsening of consciousness, new brainstem signs, or presentation in coma. Statistical analysis was performed utilizing a tree-based model fitted by binary recursive partitioning. Ninety-five percent confidence intervals (CI) were calculated. RESULTS: The overall probability of surgical intervention was 33% (CI 23-43%). The chance of surgery in stable patients was 7% (CI 2-20%). Neurologic deterioration was seen in 54 patients (57%) and increased the prospects of a surgical procedure (52%, CI 38-66%). Surgery was performed in all deteriorating patients with small hematomas (size <3 cm), but large clots (size >3 cm) did not substantially influence surgical decision-making (45%, CI 30-60%) except in patients younger than 70 years old (57%, CI 41-82%). CONCLUSIONS: Clinicians at our institution usually wait for clinical deterioration to unfold prior to operating on patients with cerebellar hematomas. After deterioration occurs, they prefer small hematomas but will operate on large hematomas when patients are younger than 70, generally withholding surgery from older patients. These attitudes may impact on outcome and should be considered in future treatment trials.

Relationship between antimalarial drug activity, accumulation, and inhibition of heme polymerization in Plasmodium falciparum in vitro.

We have investigated the contribution of drug accumulation and inhibition of heme polymerization to the in vitro activities of a series of antimalarial drugs. Only those compounds exhibiting structural relatedness to the quinolines inhibited heme polymerization. We could find no direct correlation between in vitro activity against chloroquine-susceptible or chloroquine-resistant isolates and either inhibition of heme polymerization or cellular drug accumulation for the drugs studied. However, in vitro activity against a chloroquine-susceptible isolate but not a chloroquine-resistant isolate showed a significant correlation with inhibition of heme polymerization when the activity was normalized for the extent of drug accumulation. The importance of these observations to the rational design of new quinoline-type drugs and the level of agreement of these conclusions with current views on quinoline drug action and resistance are discussed.

MR imaging of the lumbar spine: enhancement of the radicular veins.

Enhancement of lumbar nerve roots in the setting of degenerative disk disease has been considered by several authors as evidence of a breakdown in the blood-nerve barrier induced by nerve root compression [1-3]. Unfortunately, correlation between radicular enhancement and the clinically determined level of radiculopathy has not been consistently shown [4, 5]. We recently proposed that this phenomenon represents intravascular enhancement of radicular veins that travel adjacent to or within the endoneurium of one or more nerve roots of the cauda equina [4, 5]. Our purpose in this pictorial essay is to illustrate the appearance of radicular vein enhancement so that this phenomenon will not be misinterpreted as being clinically significant in the setting of degenerative disk disease.

Anesthetic blockade of the dorsolateral funiculus enhances evoked activity of spinal cord dorsal horn neurons.

1. A previous study of cat lumbar dorsal horn neurons found reduced responsiveness to A-fiber stimulation 1.5-12 h after thoracic dorsolateral funiculus (DLF) lesions. The present study was undertaken to determine whether this was due to the loss of descending activity or to factors specifically associated with injury by examining the response properties of dorsal horn cells before and during lidocaine blockade of the ipsilateral DLF. Electric shocks applied to the dorsal columns were used to search for dorsal horn cells. Noxious and nonnoxious cutaneous mechanical stimuli and graded electrical stimuli applied to the tibial nerve were used to activate peripheral afferent fibers. Cells were classed as low threshold (LT), high threshold (HT), or multireceptive (MR), according to their responses to natural stimuli. Baseline data were collected from a total of 58 cells. Twelve of these were further studied after lidocaine injection of the DLF. All cells examined with lidocaine were in dorsal horn laminae III-V. 2. All cells responded to activation of tibial nerve A fibers. However, the median threshold for the HT and MR cells (200 microA) was significantly higher than that of the LT cells (75 microA). Some cells in each class were also activated by C fibers (10, 70, and 64% of the LT, HT, and MR cells, respectively). 3. For the cells that were further characterized by lidocaine blockade of the DLF, all LT cells (n = 3) responded only to A-fiber stimulation, and all HT (n = 3) and MR cells (n = 6) responded to both A- and C-fiber stimulation. 4. For LT cells, responses evoked by mechanical and electrical stimuli were unaltered by lidocaine blockade. 5. HT and MR cells showed enhanced responses to electrical stimulation of C fibers during DLF blockade. There was no consistent effect of the blockade on A-fiber-evoked responses. 6. Two of three HT and four of six MR cells studied with lidocaine had spontaneous activity, which exhibited a small but significant increase during DLF blockade. 7. Receptive fields for noxious stimulation expanded in two of six MR cells during DLF blockade. Two of three HT cells developed responses to tactile stimuli during the blockade. 8. In two additional cells (1 HT and 1 MR), spontaneous activity and responses to C-fiber input increased after the DLF was cut.(ABSTRACT TRUNCATED AT 400 WORDS)