Daily Archives: August 20, 2014

Membrane pore-size distribution using evapoporometry

Measuring pore-distribution of low-pressure membranes has been a challenge. This technique may push the science forward.

Akhondi, E. Wicaksana, F., Krantz, W.B., Fane, A.G. Evapoporometry determination of pore-size distribution and pore fouling of hollow fiber membranes. Journal of Membrane Science 2014-11-15 470:334-345

Hollow fiber (HF) membranes are used in many applications for which characterization of the pore-size distribution (PSD) is necessary. Current techniques for determining the PSD require relatively expensive dedicated equipment. Moreover, most techniques are not applicable for characterization of fouled membranes. Evapoporometry (EP) is a novel characterization technique based on vapor-pressure depression that can detect the full spectrum of pore sizes in ultrafiltration (UF) membranes. In prior studies EP was used to determine the PSD of only flat sheet membranes using just isopropyl alcohol (IPA) as the volatile wetting test liquid. Here it is extended to HF membranes using both IPA and water as the test liquids. The average pore diameter of polyvinylidene fluoride (PVDF) HF membranes using IPA and water as the test liquids was 30.2±1.4nm and 27.4±2.0nm, respectively. The average pore diameter using IPA and water for polyacrylonitrile (PAN) HF membranes was 11.8±1.0nm and 12.1±2.8nm, respectively. Liquid displacement porometry (LDP) gave a markedly smaller average pore diameter of 20.7±3.8nm for the PVDF membranes compared to evaluating the pore diameter with EP owing to compaction under displacement pressures as high as 6MPa. LDP gave a substantially larger average pore diameter of 26.5±1.0nm for the PAN membranes compared to evaluating the pore diameter with EP owing to its inability to characterize pores smaller than 14nm. EP characterization of the PSD before and after fouling the PVDF membrane with humic acid and bentonite showed a 35% reduction in the effective average pore diameter owing to internal pore fouling.

Click here for full paper (Open Access).

 

Solar activity more plausible for regulation of Northern Hemisphere Temperatures

There is a good discussion of this paper here.

Wernicke, J., Grießinger, J., Hochreuther, P., and Bräuning, A.: Variability of summer humidity during the past 800 years on the eastern Tibetan Plateau inferred from δ18O of tree-ring cellulose, Clim. Past Discuss., 10, 3327-3356, doi:10.5194/cpd-10-3327-2014, 2014.

We present an 800 years long δ18O chronology from the eastern part of the Tibetan Plateau (TP). The chronology dates back to 1193 AD and was sampled in 1996 AD from living Juniperus tibetica trees. The chronology is unique for eastern Tibet and provides a reliable archive for hydroclimatic reconstructions. Highly significant correlations were obtained with air moisture (relative humidity, vapour pressure and precipitation) during the summer season. We applied a linear transfer model to reconstruct the summer season relative humidity variation over the past 800 years. We identified more moist conditions at the termination of the Medieval Warm Period, an oscillating air humidity around the mean during the Little Ice Age and a sudden decrease of relative humidity since the 1870s. The late 19th century humidity decrease is in good accordance with several multiproxy hydroclimate reconstructions for south Tibet. On the other hand, since the end of the 19th century strong evidences for an increase in humidity on the northern TP is exhibited. Spatial correlation analysis with the North Atlantic Oscillation index (NAO) and the sea surface temperature (SST) of Niño region 3.4 reveal a weak and nonstationary relationship to the δ18O chronology. Instead, spatial correlations expose a dominating convective influence to the relative humidity reconstruction. Furthermore, wavelength analysis reveal good agreements between the significant cyclicities in our δ18O chronology and several moisture sensitive proxy archives.

Click here for the “Discussion” version of the full paper (Open Source).

 

Skeptics of climate science are more scientifically educated

Kahan, Dan M. and Wittlin, Maggie and Peters, Ellen and Slovic, Paul and Ouellette, Lisa Larrimore and Braman, Donald and Mandel, Gregory N., The Tragedy of the Risk-Perception Commons: Culture Conflict, Rationality Conflict, and Climate Change (2011). Temple University Legal Studies Research Paper No. 2011-26; Cultural Cognition Project Working Paper No. 89; Yale Law & Economics Research Paper No. 435; Yale Law School, Public Law Working Paper No. 230. Available at SSRN: http://ssrn.com/abstract=1871503 or http://dx.doi.org/10.2139/ssrn.1871503

The conventional explanation for controversy over climate change emphasizes impediments to public understanding: Limited popular knowledge of science, the inability of ordinary citizens to assess technical information, and the resulting widespread use of unreliable cognitive heuristics to assess risk. A large survey of U.S. adults (N = 1540) found little support for this account. On the whole, the most scientifically literate and numerate subjects were slightly less likely, not more, to see climate change as a serious threat than the least scientifically literate and numerate ones. More importantly, greater scientific literacy and numeracy were associated with greater cultural polarization: Respondents predisposed by their values to dismiss climate change evidence became more dismissive, and those predisposed by their values to credit such evidence more concerned, as science literacy and numeracy increased. We suggest that this evidence reflects a conflict between two levels of rationality: The individual level, which is characterized by citizens’ effective use of their knowledge and reasoning capacities to form risk perceptions that express their cultural commitments; and the collective level, which is characterized by citizens’ failure to converge on the best available scientific evidence on how to promote their common welfare. Dispelling this, “tragedy of the risk-perception commons,” we argue, should be understood as the central aim of the science of science communication.

Click here for full paper (Open Access).