How reproducible are surface areas calculated from the BET equation?

Porosity and surface area analysis play a prominent role in modern materials science. At the heart of this sits the Brunauer-Emmett-Teller (BET) theory, which has been a remarkably successful contribution to the field of materials science. The BET method was developed in the 1930s for open surfaces but is now the most widely used metric for the estimation of surface areas of micro- and mesoporous materials. Despite its widespread use, the calculation of BET surface areas causes a spread in reported areas, resulting in reproducibility problems in both academia and industry. To prove this, for this analysis, 18 already-measured raw adsorption isotherms were provided to sixty-one labs, who were asked to calculate the corresponding BET areas. This round-robin exercise resulted in a wide range of values. Here, the reproducibility of BET area determination from identical isotherms is demonstrated to be a largely ignored issue, raising critical concerns over the reliability of reported BET areas. To solve this major issue, a new computational approach to accurately and systematically determine the BET area of nanoporous materials is developed. The software, called "BET surface identification" (BETSI), expands on the well-known Rouquerol criteria and makes an unambiguous BET area assignment possible

Optimization Of Capture In Multiple Access Radio Systems With Rayleigh Fading And Random Power Levels

To enhance the throughput of a slotted random access protocol in a radio communication system, we describe the use of a scheme in which multiple power levels are used at the transmitters. We first consider a situation in which n transmitters are simultaneously trying to send a packet to a central receiving station using a time-slotted access protocol, like slotted ALOHA. Each of these transmitters randomly chooses one of m discrete power levels during each attempt to send a packet. One of the simultaneously sent packets can often be successfully received due to the power capture effect. In this paper, we determine the optimal transmit probabilities for the power levels as well as the optimal values of the power levels themselves, when their range is constrained and in the presence of Rayleigh fading and power capture. After determining the precise optimal power levels and probabilities for maximizing the capture probabilities (i.e., for a given n), we propose a less complex, but nearly..

Prognostic value of clinical and electrodiagnostic parameters at time of diagnosis in patients with amyotrophic lateral sclerosis

OBJECTIVE: To assess the added prognostic value of the aggregated clinical and electrodiagnostic data, which define a given diagnostic category according to the Awaji or revised El Escorial criteria at time of diagnosis in patients with amyotrophic lateral sclerosis (ALS). METHODS: Clinical signs and electrodiagnostic test results were collected at time of diagnosis in 396 patients with ALS between January 2009 and January 2016. Significant predictors of prognosis were identified using a univariate model, and later combined in a multivariate Cox regression model. RESULTS: Known factors associated with reduced survival included older age at onset, shorter diagnostic delay, higher ALSFRS-R slope and presence of C9orf72 mutation (all p < 0.05). Diagnostic category according to Awaji (p < 0.0001) or to revised El Escorial (p = 0.0177) criteria, definite ALS according to Awaji (p < 0.0001) or to revised El Escorial (p = 0.0343) and number of regions with LMN involvement (p < 0.0001) were all associated with shorter survival. DISCUSSION: Clinical and electrodiagnostic data at time of diagnosis provide additional prognostic information compared to other known prognostic factors. Diagnostic category according to Awaji and the extensiveness of LMN involvement contain the most additional value.status: publishe