High frequency UV-Vis sensors estimate error in riverine dissolved organic carbon load estimates from grab sampling

High frequency ultraviolet - visible (UV-VIS) sensors offer a way of improving dissolved organic carbon (DOC) load estimates in rivers as they can be calibrated to DOC concentration. This is an improvement on periodic grab sampling, or the use of pumped sampling systems which store samples in-field before collection. We hypothesised that the move to high frequency measurements would increase the load estimate based on grab sampling due to systemic under-sampling of high flows. To test our hypotheses, we calibrated two sensors in contrasting catchments (Exe and Bow Brook, UK) against weekly grab sampled DOC measurements and then created an hourly time series of DOC for the two sites. Taking this measurement as a 'true' value of DOC load, we simulated 1,000 grab sampling campaigns at weekly, fortnightly and monthly frequency to understand the likely distribution of load and error estimates. We also performed an analysis of daily grab samples collected using a pumped storage sampling system with weekly collection. Our results show that: a) grab sampling systemically underestimates DOC loads and gives positively skewed distributions of results, b) this under-estimation and positive skew decreases with increasing sampling frequency, c) commonly used estimates of error in the load value are also systemically lowered by the oversampling of low, stable flows due to their dependence on the variance in the flow-weighted mean concentration, and d) that pumped storage systems may lead to under-estimation of DOC and over estimation of specific ultra-violet absorbance (SUVA), a proxy for aromaticity, due to biodegradation during storage.

Dysembryoplastic neuroepithelial tumors in childhood: long-term outcome and prognostic features

BACKGROUND

Dysembryoplastic neuroepithelial tumors (DNTs) are associated with medically intractable epilepsy and a favorable prognosis after surgical resection. The authors describe the clinical, radiologic, and pathologic characteristics and outcomes in children after surgical resection of pathologically confirmed DNT to ascertain prognostic features for seizure recurrence following surgery.

METHODS

Neurology, neurosurgery, and pathology databases from 1993 to 2002 at the Hospital for Sick Children were searched to retrospectively identify children with confirmed DNT and presentation with seizures. Risk factors for postoperative seizure recurrence were examined with respect to seizure outcome at 12 months and long-term follow-up.

RESULTS

Of the 26 children identified (mean age at surgery 10.0 years) seizure outcome was good in 22 children (85%) at 12 months (Class 1). At longer follow-up (mean 4.3, range 1.0 to 11.0 years) only 16 (62%) remained seizure-free. Residual DNT was evident in 15 of the 24 children with available postoperative MRI. Three children demonstrated recurrence of tumor. At 12 months follow-up, older age (>10 years) and longer duration of epilepsy (>2 years) were associated with seizure recurrence. The presence of residual tumor was a risk factor for seizure recurrence at long-term follow-up (p = 0.02).

CONCLUSIONS

Children with DNT and epilepsy may benefit from surgical management; however, seizure outcome is not always favorable. Although the majority of children remain seizure free after surgical excision of DNT, a considerable number have recurrent seizures. Short-term outcome is influenced by older age at surgery and longer duration of epilepsy. Residual tumor is a significant risk factor for poor seizure outcome. Recurrent tumor can occur.

Medical students' attitudes toward physician-assisted suicide

CONTEXT

In November 1994, Oregon became the first US state to legalize physician-assisted suicide (PAS) as an option for end-of-life care.

OBJECTIVE

This study compares the attitudes and experiences of medical students in Oregon regarding PAS to those of fourth-year medical students in the United States outside Oregon.

DESIGN

A survey of all students at the Oregon Health Sciences University and fourth-year medical students at 3 non-Oregonian US medical schools.

PARTICIPANTS

Oregon medical students returned 227 questionnaires (58%), and 113 were returned from control schools (33%).

RESULTS

A similar percentage of both study groups favored the legalization of PAS (64% vs 66%; P = .74). If the practice were legal, 55% of the total surveyed reported they "might be willing to write a lethal prescription," (50% Oregon students vs 60% control; P = .13 and 44% fourth-year Oregon students vs 60% control; P = .04). Among fourth-year students, 20% reported a request by a patient to the student or a preceptor for a lethal prescription in the past year (26% vs 16%; P = .09).

CONCLUSIONS

This study demonstrates support for and willingness by many medical students to participate in PAS. Some medical students reported observation of PAS during their training experience. Fourth-year Oregon students reported significantly less willingness than other students to provide a patient with a lethal prescription, perhaps indicating hesitancy to include PAS in clinical practice.

Prevalence of harassment and discrimination among 1996 medical school graduates: a survey of eight US schools

CONTEXT

Harassing and discriminating behaviors on the part of instructors or supervisors are known to affect the quality of work performed by medical students, influence their career decisions, and have other undetermined long-term consequences.

OBJECTIVE

To assess the prevalence and forms of harassment and discrimination experienced by 1996 medical school graduates.

DESIGN

A self-administered survey of harassment and discrimination mailed to graduating medical students.

SETTING AND PARTICIPANTS

A total of 1001 graduating medical students at 8 US medical schools (4 public and 4 private), chosen from each of the 4 regions designated by the Association of American Medical Colleges for geographic categorization.

OUTCOME MEASURE

The number of reported experiences of various forms of harassment and discrimination while attending medical school.

RESULTS

Of 1001 surveys, 548 (55%) were returned. Overall, 46% of the students reported experiencing some form of harassment and 41% some form of discrimination from instructors or supervisors while attending medical school. Nonsexual verbal harassment was reported by 41%; sexual verbal harassment was reported by 10%. Discrimination based on gender was reported by 29% of students; discrimination based on race was reported by 12%.

CONCLUSIONS

Harassment and discrimination of medical students by instructors and supervisors continue to occur frequently, and new approaches are needed to address these problems.

Cytosolic protein kinase A mediates the growth hormone (GH)-releasing action of GH-releasing factor in purified rat somatotrophs

The growth hormone (GH)-releasing action of GH-releasing factor (GRF) is known to be cAMP-dependent. However, definitive proof for the involvement of the cAMP-dependent enzyme protein kinase A (PKA) is still lacking. In this study, we characterized the PKA system in purified rat somatotrophs and examined its role in mediating GRF-stimulated GH release under static incubation conditions. PKA enzyme activity was detected only in the cytosolic, but not the particulate fraction of rat somatotrophs. This cytosolic PKA activity exhibited the characteristic cAMP dependence (with ED50 of 0.1 microM), ability to phosphorylate kemptide (a synthetic peptide with a PKA phosphorylation site), and susceptibility to inhibition by the bovine heat-stable PKA inhibitor. GRF treatment (1 pM-1 nM) stimulated the cytosolic PKA activity and GH release from rat somatotrophs in a dose-dependent manner. Time-course studies also demonstrated that activation of cAMP synthesis and PKA activity preceded the GH response to GRF. Stimulation of cytosolic PKA activity in rat somatotrophs by the adenylate cyclase activator forskolin (10 nM-1 microM) and membrane permeant cAMP analog db.cAMP (5 microM-0.5 mM) mimicked the GH-releasing effect of GRF. In contrast, Rp.cAMP, a cAMP antagonist for PKA regulatory subunits, blocked both the cytosolic PKA activity as well as GRF-induced GH release. Similar inhibitions were also observed when an inhibitor for PKA catalytic subunits, H89, was used. Somatostatin (SRIF) (1 nM), the physiological GH-release inhibitor, suppressed the GH response to GRF without affecting the basal or GRF-stimulated PKA activity. SRIF at a higher dose (10 nM) abolished the GH-releasing effect of GRF. In this case, SRIF also induced a small but significant inhibition of GRF-stimulated PKA activity. Taken together, the present study provides direct evidence that PKA enzyme activity is localized only in the cytosol of rat somatotrophs and constitutes an essential component of the signal transduction mechanism for GRF-stimulated GH release. This cytosolic PKA system, however, does not appear to be a major target for the GH-release inhibiting action of SRIF.

Patterns of transmission in measles outbreaks in the United States, 1985-1986

Since the licensing of measles vaccine in 1963, the incidence of reported measles in the United States has declined to less than 2 percent of previous levels. To characterize the current epidemiology of measles in the United States, we analyzed measles outbreaks that occurred during 1985 and 1986. There were 152 outbreaks (defined as five or more cases related epidemiologically), which accounted for 88 percent of the cases reported during those two years. There were two major types of outbreaks: those in which most of the cases occurred among preschool-age children (those under 5 years of age) (26 percent) and those in which most of the cases occurred among school-age persons (those 5 to 19 years of age) (67 percent). The outbreaks among preschool-age children ranged in size from 5 to 945 cases (median, 13); a median of only 14 percent of the cases occurred in vaccinated persons, and a median of 45 percent of the cases were classified as preventable according to the current strategy. Outbreaks among school-age persons ranged in size from 5 to 363 cases (median, 25); a median of 60 percent of the cases occurred in vaccinated persons, and a median of only 27 percent of the cases were preventable. The outbreaks among preschool-age children indicate deficiencies in the implementation of the national measles-elimination strategy. However, the extent of measles transmission among highly vaccinated school-age populations suggests that additional strategies, such as selective or mass revaccination, may be necessary to prevent such outbreaks.

International measles importations United States, 1980-1985

Between 1980 and 1985, 89-121 international measles importations were reported annually in the US, accounting for 0.7-6.9% of the annual number of reported measles cases. These measles cases were acquired in more than 70 different countries. Three countries accounted for over one third of all imported cases: Mexico, the UK and the Philippines. Thirty-six states reported importations. However, over half of all importations were reported from only six states: California, New York, Maryland, Florida, Texas and Hawaii. Most measles importations did not cause transmission in the US. In 1982 and 1985 only 16% and 29% of importations resulted in any spread cases. Until there is better control of measles worldwide, high immunization levels are crucial for continued measles control in the US.

Effects of halogenated organic compounds on photosynthesis in estuarine phytoplankton

Chlorine oxidants (chlorine gas, sodium hypochlorite, and calcium hypochlorite) are used as biocides to control fouling in seawater cooled power generating plants and to kill pathogens in sewage effluents entering estuarine waters. Organisms killed include algae, fungi, bacteria, barnacles, oysters, and clams. Use of these chemicals in saline waters results in the formation of halogenated by-products (JOHANNESSON 1958, DUURSAM & PARSI 1976, DOVE 1973). BEAN et al, (1978), in a study of chlorinated seawater, identified eighteen organic compounds generated by chlorination. Due to rapid substitution of bromine for chlorine, brominated rather than chlorinated by-products are formed (FARKAS et al. 1949, GALAL-GORCHEV & MORRIS 1965, MACALADY et al. )977, SUGAM & HELZ 1977). The effects of these chlorinated by-products on estuarine phytoplankton are not known. Experiments in this study examined singly the effects of fifteen commercially available compounds on photosynthesis by estuarine phytoplankton.