Total Variation Wavelet-Based Medical Image Denoising

We propose a denoising algorithm for medical images based on a combination of the total variation minimization scheme and the wavelet scheme. We show that our scheme offers effective noise removal in real noisy medical images while maintaining sharpness of objects. More importantly, this scheme allows us to implement an effective automatic stopping time criterion

Growth and characterization of two-dimensional carbon nanostructures

Ph.DDOCTOR OF PHILOSOPH

Gendered Effects of the Minimum Wage

Women are more likely to work in jobs with low hours than men. Low-hour jobs are associated with lower hourly wages and are more likely impacted by minimum wages that set a floor on hourly wages. We document that the first German minimum wage significantly increased women's transition towards jobs with higher weekly hours. We construct and estimate an equilibrium search model with demographic and firm productivity heterogeneity. The model replicates observed gender gaps in employment, hours and wage and the positive relationship between hours and hourly wages. We implement the minimum wage in our model with a penalty to address non-compliance. Based on our model, the minimum wage primarily reduces the gender income gap through the gender wage gap. At its 2022 level, the German minimum wage reduces the gender employment and hours gap due to an upward reallocation effect, resulting in women's increased participation in higher-hour jobs with lower separation rates. The upward reallocation effect is the strongest for women with children and varies by marital state and spousal income. While the minimum wage only modestly discourages firms from posting jobs, it shifts job offers toward full-time positions

How electronic word of mouth dynamically influences product sales and supplies: an evidence from China film industry

As an important part of e-commerce, online reviews play a significant role in consumers’ purchase decisions. This study investigated the dynamic effects of electronic word of mouth (eWOM) and the number of people wishing to watch a movie on movie sales and supplies in the Chinese movie market. Using a dynamic simultaneous equation system and data of 76 films, this study analyzed the interrelationships between eWOM and movie sales and supplies. Our findings showed that both the volume and valence of eWOM affected movie sales and supplies significantly. The number of people who wanted to watch a movie had an opposite effect on movie sales and supply; eWOM volume had a positive impact on movie sales and supplies; and eWOM valence had a negative impact on movie sales and a positive impact on movie supplies. The number of people who wish to watch a movie was another important variable for movie sales and supplies, and it had a negative impact on the daily movie sales but a positive impact on the daily movie supplies. This study provided a detailed explanation of these results and thus contributed to improving the efficiency of movie suppliers’ utilization of online reviews

Interference enhancement of Raman signal of graphene

Raman spectroscopic studies of graphene have attracted much interest. The G-band Raman intensity of a single layer graphene on Si substrate with 300 nm SiO2 capping layer is surprisingly strong and is comparable to that of bulk graphite. To explain this Raman intensity anomaly, we show that in addition to the interference due to multiple reflection of the incident laser, the multiple reflection of the Raman signal inside the graphene layer must be also accounted for. Further studies of the role of SiO2 layer in the enhancement Raman signal of graphene are carried out and an enhancement factor of ~30 is achievable, which is very significant for the Raman studies. Finally, we discuss the potential application of this enhancement effect on other ultra-thin films and nanoflakes and a general selection criterion of capping layer and substrate is given.Comment: 13 pages, 3 figures to be published in Applied Physics Letter

Analysis of optical absorption in GaAs nanowire arrays

In this study, the influence of the geometric parameters on the optical absorption of gallium arsenide [GaAs] nanowire arrays [NWAs] has been systematically analyzed using finite-difference time-domain simulations. The calculations reveal that the optical absorption is sensitive to the geometric parameters such as diameter [D], length [L], and filling ratio [D/P], and more efficient light absorption can be obtained in GaAs NWAs than in thin films with the same thickness due to the combined effects of intrinsic antireflection and efficient excitation of resonant modes. Optimized geometric parameters are obtained as follows: D = 180 nm, L = 2 μm, and D/P = 0.5. Meanwhile, the simulation on the absorption of GaAs NWAs for oblique incidence has also been carried out. The underlying physics is discussed in this work