Search results for "Spreading"
showing 10 items of 91 documents
LoRa Technology Demystified: From Link Behavior to Cell-Level Performance
2020
In this paper we study the capability of LoRa technology in rejecting different interfering LoRa signals and the impact on the cell capacity. First, we analyze experimentally the link-level performance of LoRa and show that collisions between packets modulated with the same Spreading Factor (SF) usually lead to channel captures, while different spreading factors can indeed cause packet loss if the interference power is strong enough. Second, we model the effect of such findings to quantify the achievable capacity in a typical LoRa cell: we show that high SFs, generally seen as more robust, can be severely affected by inter-SF interference and that different criteria for deciding SF allocati…
Mikrokokoistetut leviämisvastus- ja nelipisteanturimittaukset puolijohderakenteen varauksenkuljettajien syvyysjakaumien määrittämisessä
2013
Entistä pienemmät puolijohderakenteet vaativat analyysityökaluilta erittäin hyvää herkkyyttä, jonka on myös kehityttävä rakenteiden vaatimusten mukaisesti -- muussa tapauksessa kehitys voi hidastua hyvin paljon ilman kunnollista tietoa valmistusmenetelmien tuloksista. Yksi oleellinen osa rakenteiden analysoimisessa on tieto seostusatomien ja varauksenkuljettajien pitoisuuksista rakenteen syvyyssuunnassa, eli syvyysjakauma. Vuosikymmeniä syvyysjakauman mittaukseen on käytetty leviämisvastusmittausta (SRP, engl. Spreading Resistance Profiling), ja nelipisteanturimittausta (4PP, engl. Four Point Probe) on käytetty kuvaamaan koko syvyysjakauman vaikutusta sähköisessä kontaktissa. Molempien tekn…
Occurrence of Spontaneous Cortical Spreading Depression Is Increased by Blood Constituents and Impairs Neurological Recovery after Subdural Hematoma …
2019
Acute subdural hemorrhage (ASDH) is common and associated with severe morbidity and mortality. To date, the role of spontaneous cortical spreading depression (sCSD) in exaggerating secondary injury after ASDH, is poorly understood. The present study contains two experimental groups: First, we investigated and characterized the occurrence of sCSD after subdural blood infusion (300 μL) via tissue impedance (IMP) measurement in a rat model. Second, we compared the occurrence and influence of sCSD on lesion growth and neurological deficit in the presence and absence of whole blood constituents. In the first experimental group, three IMP traits could be distinguished after ASDH: no sCSD, recurre…
Cluster analysis of mrna expression levels identifies multiple sequential patterns following focal cerebral ischemia
2012
AIM The purpose of this study is to detect gene expression patterns following focal cerebral ischemia. MATERIAL AND METHODS 25 male Wistar rats were divided into control (n = 8) and ischemic (n = 17) groups. In the ischemic group, slowly progressing focal ischemia was simulated by two-vein occlusion with spreading depression (SD) a cortical microinjection of KCl induced. Ischemic tissue was removed at 2, 8, 24, or 72 h postischemia. Using semiquantitative reverse transcription polymerase chain reaction, we investigated mRNA expression levels of 13 representative genes related to cerebral ischemia. Cluster analysis of the gene expression levels was done. RESULTS In the ischemic group, the ex…
Neuroprotective effect of ceftriaxone on the penumbra in a rat venous ischemia model.
2012
Glutamate transporter-1 (GLT-1) maintains low concentrations of extracellular glutamate by removing glutamate from the extracellular space. It is controversial, however, whether upregulation of GLT-1 is neuroprotective under all ischemic/hypoxic conditions. Recently, a neuroprotective effect of preconditioning with a β-lactam antibiotic ceftriaxone (CTX) that increases expression of GLT-1 has been reported in animal models of focal ischemia. On the other hand, it is said that CTX does not play a neuroprotective role in an in vitro study. Thus, we examined the effect of CTX on ischemic injury in a rat model of two-vein occlusion (2VO). This model mimics venous ischemia during, e.g. tumor sur…
Electrophysiology and neuronal integrity following systemic arterial hypotension in a rat model of unilateral carotid artery occlusion.
2007
Patients with carotid artery stenosis may be particularly susceptible to hypotension-associated cerebral ischemia and subsequent neurological sequelae. Measuring somatosensory evoked potentials (SEP), electroencephalogram (EEG), direct current (DC) potential, and histology, we compared the temporal evolution of cortical functional perturbations as well as neuronal integrity in a model of unilateral carotid artery occlusion and systemic hypobaric hypotension (HH) at the lower limit of cerebral blood flow autoregulation (50 mm Hg). Serial measurements of EEG power spectra as well as SEP-amplitudes and latencies of N10.3 were performed before, during, and up to 60 min after 30 min-HH (n=7) or …
Effects of Cortical Spreading Depression on Cortical Blood Flow, Impedance, DC Potential, and Infarct Size in a Rat Venous Infarct Model
2000
A cortical venous infarction model has been evaluated as to the degree of regional flow reduction and by studying effects of cortical spreading depression (CSD). Two adjacent cortical veins were occluded photochemically with rose bengal and fiberoptic illumination. Seven rats served to demonstrate effects on regional cortical blood flow using laser Doppler scanning. In 36 rats local CBF, DC potential, and brain tissue impedance were measured continuously for 75 min after vein occlusion. No, 3, or 10 CSD waves were induced by potassium chloride injection during the initial 75 min. Rats were compared for spontaneous CSDs; baseline local CBF, CBF, and impedance response to CSD; and infarct vol…
Calcium and increase excitability promote tolerance against anoxia in hippocampal slices.
1999
We have previously demonstrated that anoxic preconditioning (APC) protects against a subsequent otherwise 'lethal' anoxic insult in hippocampal slices. Tested here are two hypotheses: (a) APC requires calcium to improve electrical recovery in hippocampal slices; and (b) mild excitation promotes preconditioning neuroprotection. Control hippocampal slices were given a single 'test' anoxic insult followed by reoxygenation. Experimental slices were preconditioned by three short anoxic insults of 1 min separated by 10 min of reoxygenation. At 30 min after the third 'conditioning' insult, slices underwent a 'test' anoxic insult [1 min of anoxic depolarization (AD)], and then slices were reoxygena…
Spontaneous Cortical Spreading Depression and Intracranial Pressure Following Acute Subdural Hematoma in a Rat
2012
Acute subdural hemorrhage (ASDH) is a frequent and devastating consequence of traumatic brain injury. Tissue damage develops rapidly and makes treatment even more difficult. Management of increased intracranial pressure (ICP) due to extravasated blood volume and brain swelling is often insufficient to control all adverse effects of ASDH. In addition to sheer volume, spontaneously triggered cortical spreading depression (CSD) that leads to cell death following ischemia or trauma may contribute to injury development after ASDH. Therefore, we explored the occurrence of CSD by tissue impedance (IMP) measurement in a rat model subjected to ASDH. IMP and intraventricular and mean arterial pressur…
Rare-earth elements and yttrium distributions in mangrove coastal water systems: The western Gulf of Thailand
2005
The concentration of rare-earth elements and yttrium (REY) was investigated in dissolved phase, suspended particulate matter, and seafloor sediments of the western coastal area of the Gulf of Thailand. The samples show Eu and Gd positive anomalies in the shale-normalized REY patterns, especially in the suspended particulate matter. On the other hand, a very high REE content was detected in the coastal waters, probably due to the weathering produced by the Mae Klong river waters on rare-earth element (REE)-rich accessory minerals coming from terrains and mineral deposits cropping out in the studied area. The shale-normalized patterns of yttrium and REE estimated for the dissolved phase show …