Constraining the complex refractive index of black carbon particles using the complex forward-scattering amplitude

Black carbon is the largest contributor to global aerosol’s shortwave absorption in the current atmosphere and is an important positive climate forcer. The complex refractive index, m = mr + imi, the primary determinant of the absorbed and scattered energies of incident radiation per unit volume of particulate material, has not been accurately known for atmospheric black carbon material. An accurate value at visible wavelengths has been difficult to obtain due to the black carbon’s wavelength-scale irregularity and variability of aggregate shape, distribution in particle size, and mixing with other aerosol compounds. Here, we present a method to constrain a plausible (mr, mi) domain for black carbon from the observed distribution of the complex forward-scattering amplitude S(0°). This approach suppresses the biases due to the above-mentioned complexities. The S(0°) distribution of black carbon is acquired by performing single particle S(0°) measurements in a water medium after collecting atmospheric aerosols into water. We demonstrate the method operating at λ = 0.633 μm for constraining the refractive index of black carbon aerosols in the north-western Pacific boundary layer. From the plausible (mr, mi) domain consistent with the observed S(0°) distributions and the reported range of mass absorption cross-section, we conservatively select 1.95 + 0.96i as a recommendable value of the refractive index for uncoated black carbon at visible wavelengths. The recommendable value is 0.17 larger in mi than the widely used value 1.95 + 0.79i in current aerosol-climate models, implying a ∼16% underestimate of shortwave absorption by black carbon aerosols in current climate simulations.</p

Determinants of Slow Walking Speed in Ambulatory Patients Undergoing Maintenance Hemodialysis

<div><p>Walking ability is significantly lower in hemodialysis patients compared to healthy people. Decreased walking ability characterized by slow walking speed is associated with adverse clinical events, but determinants of decreased walking speed in hemodialysis patients are unknown. The purpose of this study was to identify factors associated with slow walking speed in ambulatory hemodialysis patients. Subjects were 122 outpatients (64 men, 58 women; mean age, 68 years) undergoing hemodialysis. Clinical characteristics including comorbidities, motor function (strength, flexibility, and balance), and maximum walking speed (MWS) were measured and compared across sex-specific tertiles of MWS. Univariate and multivariate logistic regression analyses were performed to examine whether clinical characteristics and motor function could discriminate between the lowest, middle, and highest tertiles of MWS. Significant and common factors that discriminated the lowest and highest tertiles of MWS from other categories were presence of cardiac disease (lowest: odds ratio [OR] = 3.33, 95% confidence interval [CI] = 1.26–8.83, P<0.05; highest: OR = 2.84, 95% CI = 1.18–6.84, P<0.05), leg strength (OR = 0.62, 95% CI = 0.40–0.95, P<0.05; OR = 0.57, 95% CI = 0.39–0.82, P<0.01), and standing balance (OR = 0.76, 95% CI = 0.63–0.92, P<0.01; OR = 0.81, 95% CI = 0.68–0.97, P<0.05). History of fracture (OR = 3.35, 95% CI = 1.08–10.38; P<0.05) was a significant factor only in the lowest tertile. Cardiac disease, history of fracture, decreased leg strength, and poor standing balance were independently associated with slow walking speed in ambulatory hemodialysis patients. These findings provide useful data for planning effective therapeutic regimens to prevent decreases in walking ability in ambulatory hemodialysis patients.</p></div

Flow diagram of the participant selection and exclusion process.

<p>Flow diagram of the participant selection and exclusion process.</p

Univariable logistic regression analysis for the discrimination between the lowest tertile vs. the middle and highest tertiles of maximum walking speed.

<p>Univariable logistic regression analysis for the discrimination between the lowest tertile vs. the middle and highest tertiles of maximum walking speed.</p

Differences in the clinical characteristics, maximum walking speed, and motor function across tertiles of maximum walking speed.

<p>Differences in the clinical characteristics, maximum walking speed, and motor function across tertiles of maximum walking speed.</p

Patient characteristics, walking speed, and motor function.

<p>Patient characteristics, walking speed, and motor function.</p

Stepwise multivariable logistic regression analysis for the discrimination between the lowest tertile vs. the middle and highest tertiles of maximum walking speed, and between the lowest and middle tertiles vs. the highest tertile of maximum walking speed.

<p>Stepwise multivariable logistic regression analysis for the discrimination between the lowest tertile vs. the middle and highest tertiles of maximum walking speed, and between the lowest and middle tertiles vs. the highest tertile of maximum walking speed.</p

Histogram of maximum walking speed.

<p>Maximum walking speed was calculated in meters per minute. Open and closed bars indicate women and men, respectively.</p

Additional file 3: Table S3. of Determinants of difficulty in activities of daily living in ambulatory patients undergoing hemodialysis

Univariate and multivariate logistic regression analyses on ADL difficulty. Univariate and multivariate logistic regression analyses were performed with ADL difficulty as a dependent variable and age, male sex, blood hemoglobin concentration, serum albumin concentration, comorbidity index, depression symptoms, maximum leg strength, one-leg standing time, and usual walking speed as independent variables for each level. *ADL items with higher level difficulty included “walking up two flights of stairs,” “walking 1 km,” “walking 600 m,” and “rising from the floor.” †ADL items with middle level difficulty included “walking down two flights of stairs,” “walking 300 m,” “walking up one flight of stairs,” and “sitting down on the floor.” ‡ADL items with lower level difficulty included “walking 20 m quickly,” “walking down one flight of stairs,” “walking 100 m,” and “rising from a chair.” ADL, activities of daily living; OR, odds ratio; CI, confidence interval. (XLSX 15 kb

Additional file 2: Table S2. of Determinants of difficulty in activities of daily living in ambulatory patients undergoing hemodialysis

Clinical characteristics, motor function, ADL dependency, and ADL difficulty of study subjects. Data are presented as mean ± standard deviation or number of subjects. *ADL items with higher level difficulty included “walking up two flights of stairs,” “walking 1 km,” “walking 600 m,” and “rising from the floor.” †ADL items with middle level difficulty included “walking down two flights of stairs,” “walking 300 m,” “walking up one flight of stairs,” and “sitting down on the floor.” ‡ADL items with lower level difficulty included “walking 20 m quickly,” “walking down one flight of stairs,” “walking 100 m,” and “rising from a chair.” BMI, body mass index: HD, hemodialysis; ADL, activities of daily living. (XLSX 17 kb