Pyrolysis of white pine

Pyrolysis of white pine wood has been studied in thin samples (1.6 mm thick slabs) exposed in an oven at 199–365°C and in thick samples (8–50 mm diam branch segments) exposed in a wind tunnel at 365–525°C and 3–18 m/s wind speed. In the limit case of sufficiently low temperatures and thin samples, the mass-loss rate is kinetically controlled. The kinetics is effectively first order. Mass-loss histories of thin samples above 150–200°C are divided into a short initial period with high rate coefficient, a long middle period with medium rate coefficient, and a final indefinitely long period with very low rate coefficient. Energies of activation $\text{E}\text{R}\text{= 13.3}\text{kK}$ at 93–200°C and 16.3 kK at 200–365°C are inferred. Evidence is given that in thick samples at low temperatures pyrolysis and heat transfer are not very strongly coupled, mass loss being fairly well predicted by first calculating temperature fields as in the case of no chemcial reaction and then computing pyrolysis rates from the kinetic results with due allowance for temperature variation.     

Performance of simulcast wireless techniques for personalcommunication systems

Broadband analog transport facilities using fiber or fiber/coax cable can play a significant role in the evolution of the network infrastructure for personal communications services (PCSs). Low-power PCS systems require a dense grid of radio ports to provide connectivity to the telephone network. Analog transport has a number of important advantages over digital transmission facilities, including the flexibility to support a variety of air interface formats, shared infrastructure cost with other services such as video distribution, and centralized call processing allowing the use of low cost and simple radio ports. A simulcast technique can be used in such systems to permit low rates of handoff (no handoff within each simulcast area) and sharing of hardware resources among multiple radio ports. This paper provides a detailed model and a simulation analysis of the cochannel interference and noise performance as well as the resource sharing benefit of a simulcast PCS system. Several potential PCS air interfaces are considered, including time division multiple access (TDMA) and code division multiple access (CDMA) techniques. Our investigation shows that the impact of multiple antenna noise in a simulcast system is offset by the improved signal-to-interference (SIR) ratio brought about by distributed antennas. Even with distributed antennas, multiple antenna noise places a limit on the maximum number of radio ports that can be assigned to each simulcast group. This limit, however, is shown to have little impact on the achievable resource sharing benefit of simulcasting (i.e., grouping beyond this limit has diminishing returns). A saving of 40% to 60%, in terms of the required central hardware resources, is typical for both TDMA and CDMA systems in suburban environments     

Sagittal sinus occlusion, caused by an overlying depressed cranial fracture, presenting with late signs and symptoms of intracranial hypertension: case report

A case of delayed signs of intracranial hypertension after open depressed cranial fracture occluding the superior sagittal sinus is reported. Elevating depressed fractures overlying a cranial venous sinus is hazardous. Conservative management of the intracranial hypertension, including repeated lumbar punctures, led to an unimpaired outcome. The options of management of delayed problems caused by traumatic venous occlusion are discussed.     

Neurosurgical management of cerebral aneurysms following unsuccessful or incomplete endovascular embolization

Modern endovascular techniques permit treatment of intracranial aneurysms in many circumstances when surgery is associated with significant morbidity. Occasionally, embolization of aneurysms is unsuccessful or incomplete or followed by complications, in which case surgical management is required. Since 1986, 196 patients have undergone embolization of intracranial aneurysms at the authors' institution and 21 (11%) required subsequent surgical treatment. Attempted embolization failed in five patients (Group A). Ten patients (Group B) had only partial occlusion of the aneurysm or demonstrated recanalization on follow-up studies. Eight of these Group B patients underwent embolization with Guglielmi detachable coils (GDCs), representing 5.7% of the 141 GDC-treated patients in this experience. Surgical treatment in these two groups consisted of clipping (eight cases), surgical parent vessel occlusion (one case), and parent vessel occlusion with extracranial-intracranial bypass (six cases). Fourteen (93%) of the 15 patients in these two groups had an excellent or good outcome with complete aneurysm occlusion. Six patients underwent surgery to treat complications related to the endovascular procedure (Group C). Of these, four patients had neurological improvement compared to their preoperative state, and two died. This series of cases demonstrates that surgical treatment of aneurysms is usually possible with good results following incomplete embolization and emphasizes the need for close and continued neurosurgical involvement in the endovascular management of intracranial aneurysms.     

Synthesis and characterization of 8-methoxy-2''- deoxyadenosine-containing oligonucleotides to probe the syn glycosidic conformation of 2''-deoxyadenosine within DNA

BACKGROUND: Rectal motor activity is incompletely understood. The aim of this study was to characterize the patterns of rectal motor activity and to examine their diurnal variation and their relationships to proximal colonic activity and to meals. METHODS: We performed a 30-h ambulatory motility study by recording pressure activity at multiple sites in the colon in 18 normal subjects. RESULTS: During 288 h of recording, discrete bursts of tonic and phasic activity were seen in the rectum of all subjects at night and during the day lasting > or = 3 min, with a predominant frequency of 3 waves/min: periodic rectal motor activity (PRMA). Nocturnally, the number of cycles and the proportion of time occupied by this activity were greater (p < 0.001) and the inter-cycle interval was shorter (p < 0.008) compared with daytime, but the cycle duration was similar. Only 4 versus 5% (nocturnal vs daytime) of cycles propagated aborad, whereas 36 versus 14% (p < 0.01) propagated retrogradely, 16 versus 47% (p < 0.01) occurred simultaneously, and 44 versus 34% were confined to the rectum. There was considerable intra- and intersubject variability. PRMA was not related to meals or to anal motor activity, but 81% of nocturnal and 94% of daytime cycles occurred within 5 min of a motor event in the more proximal colon. CONCLUSIONS: PRMA is a characteristic feature of the normal rectum and is more frequent at night. The temporal association with motor events in the proximal colon suggests that PRMA is triggered by the arrival of stool or gas in the rectum. Because most cycles are either segmental or are propagated retrogradely, PRMA may serve as an intrinsic braking mechanism that prevents untimely flow of colonic contents, particularly during sleep.