A novel method based on cross sensitivity of cataluminescence (CTL) on nano-Ti3CeY2O11 was proposed for simultaneous determination of formaldehyde, benzene and sulfur dioxide in air.The relations between the concentrations of formaldehyde, benzene and sulfur dioxide and their CTL intensities were respectively ascertained at three wavelengths.The accurate concentrations of formaldehyde, benzene and sulfur dioxide can be calculated by superimposed total CTL intensities.The three analysis wavelengths are 420 nm, 535 nm and 680 nm.The surface temperature of the sensitive materials is 280℃.The carrier gas flow rate is 130 mL/min.The detection limits (3σ) are 0.04 mg/m3 for formaldehyde, 0.05 mg/m3 for benzene and 0.10 mg/m3 for sulfur dioxide, respectively.The linear ranges of CTL intensity versus analyte concentration are 0.08-75.60 mg/m3 for formaldehyde, 0.1-101.40 mg/m3 for benzene and 0.3 to 115.00 mg/m3 for sulfur dioxide.The recoveries of 12 testing standard samples by this method are 96.4%-103.7% for formaldehyde, 97.8%-102.5% for benzene and 97.2%-103.3% for sulfur dioxide.Common coexisting substances, such as acetaldehyde, toluene, hydrogen sulfide, ammonia, methanol, ethanol and carbon dioxide, do not disturb the determination.The relative deviation of CTL signals of continuous 200 h detection for gaseous mixture containing formaldehyde, benzene and sulfur dioxide is less than 2%, which shows the longevity of the nanometer composite oxide to formaldehyde, benzene and sulfur dioxide.This method makes full use of the cross sensitive phenomenon, and can realize the on-line analysis of formaldehyde, benzene and sulfur dioxide in air.

Objective To investigate whether problem-based learning (PBL) is suitable for medical imaging and whether PBL is more enlightening than lecture-based learning (LBL) mode in teaching of medical imaging.Methods Thirty-two students of clinical medicine specialty in Sun Yat-sen University were selected as teaching objects and were divided into 6 groups (5 students in four groups and 6students in 2 groups).Chapters of urinary and digestive system were taught by PBL mode while the rest chapters by LBL mode.Questionnaires were handed out to teachers and students by Email after class and the valid questionnaires were analyzed qualitatively.Results Thirty-one students and 5 teachers thought they were suitable for PBL teaching; 30 students and 5 teachers were willing to continue PBL.Thirty-one students and 5 teachers thought that PBL mode could let students learn more knowledge and was more revealing.Twenty-three students thought PBL teaching spent too much time can not promote in all chapters.Three teachers worried that PBL mode would cause poor organization form and teaching plans.Conclusions PBL is suitable for medical imaging teaching.PBL could let students learn more knowledge and is more revealing compared with LBL,however,PBL is time-consuming and laborious,therefore LBL and PBL should be combined.