Microrheology of colloidal dispersions: Shape matters

We consider a “probe” particle translating at constant velocity through an otherwise quiescent dispersion of colloidal “bath” particles, as a model for particle-tracking microrheology experiments in the active (nonlinear) regime. The probe is a body of revolution with major and minor semiaxes a and b, respectively, and the bath particles are spheres of radii b. The probe's shape is such that when its major or minor axis is the axis of revolution the excluded-volume, or contact, surface between the probe and a bath particle is a prolate or oblate spheroid, respectively. The moving probe drives the microstructure of the dispersion out of equilibrium; counteracting this is the Brownian diffusion of the bath particles. For a prolate or oblate probe translating along its symmetry axis, we calculate the nonequilibrium microstructure to first order in the volume fraction of bath particles and over the entire range of the Péclet number (Pe), neglecting hydrodynamic interactions. Here, Pe is defined as the non-dimensional velocity of the probe. The microstructure is employed to calculate the average external force on the probe, from which one can infer a “microviscosity” of the dispersion via Stokes drag law. The microviscosity is computed as a function of the aspect ratio of the probe, â=a/b, thereby delineating the role of the probe's shape. For a prolate probe, regardless of the value of â, the microviscosity monotonically decreases, or “velocity thins,” from a Newtonian plateau at small Pe until a second Newtonian plateau is reached as Pe-->[infinity]. After appropriate scaling, we demonstrate this behavior to be in agreement with microrheology studies using spherical probes [Squires and Brady, “A simple paradigm for active and nonlinear microrheology,” Phys. Fluids 17(7), 073101 (2005)] and conventional (macro-)rheological investigations [Bergenholtz et al., “The non-Newtonian rheology of dilute colloidal suspensions,” J. Fluid. Mech. 456, 239–275 (2002)]. For an oblate probe, the microviscosity again transitions between two Newtonian plateaus: for â3.52 the microviscosity at small Pe is less than at large Pe, which suggests it “velocity thickens” as Pe is increased. This anomalous velocity thickening—due entirely to the probe shape—highlights the care needed when designing microrheology experiments with non-spherical probes

On the bulk viscosity of suspensions

The bulk viscosity of a suspension relates the deviation of the trace of the macroscopic or averaged stress from its equilibrium value to the average rate of expansion. For a suspension the equilibrium macroscopic stress is the sum of the fluid pressure and the osmotic pressure of the suspended particles. An average rate of expansion drives the suspension microstructure out of equilibrium and is resisted by the thermal motion of the particles. Expressions are given to compute the bulk viscosity for all concentrations and all expansion rates and shown to be completely analogous to the well-known formulae for the deviatoric macroscopic stress, which are used, for example, to compute the shear viscosity. The effect of rigid spherical particles on the bulk viscosity is determined to second order in volume fraction and to leading order in the Péclet number, which is defined as the expansion rate made dimensionless with the Brownian time scale. A repulsive hard-sphere-like interparticle force reduces the hydrodynamic interactions between particles and decreases the bulk viscosity

A new resistance function for two rigid spheres in a uniform compressible low-Reynolds-number flow

The pressure moment of a rigid particle is defined as the trace of the first moment of the surface stress acting on the particle. We calculate the pressure moments of two unequal rigid spheres immersed in a uniform compressible linear flow, using twin multipole expansions and lubrication theory. Following the practice established in previous studies on two-body hydrodynamic interactions at low Reynolds number, the results are expressed in terms of a new (stresslet) resistance function

Consumers’ Perceptions, Attitudes and Willingness to Pay Towards Chemical Free Vegetable in North Sumatera

This study was aimed to determine consumers’perceptions, attitudes and willingness to pay (WTP) towards chemical free vegetable (CFV) produce in North Sumatra Province.A total of 2080 respondents were interviewed using a close-ended questionnaire.Collected data was analysed using descriptive analysis, factor analysis and contingent valuation method (CVM).The results indicated that more than half of the respondents have consumed CFV.The result showed that lack of knowledge of CFV and the place to purchase CFV were the main reasons for consumers not consuming CFV.Nutritional value was an important factor that influences consumers’preferences in purchasing CFV, followed by desire, freshness, health effect and taste.The factor analysis identified nine factors that influenced the purchase of CFV among North Sumatra Province consumers.The factors were government involvement,health consciousness,consumer influence to purchase,product availability,awareness of chemical use, product appearance,information awareness, market potential and consumer awareness to consume.Contingent Valuation Method was used to estimate consumers’ WTP for CFV.A logit and probit model was used to determine consumers’WTP a premium for CFV.The results indicate that gender, household income, price level,marital status and household member below 17 years old were the most important and significant factors that influenced and determined the amount of premium that a consumer is willing to pay for CFV.Based on the study,it was found that at present, CFV market is still a niche market,catering only to a small segment of the whole vegetable market in North Sumatra Province. Generally, North Sumatra Province consumers’ have the potential to purchase CFV produce. Thus, there is a need for the proper development of an effective CFV market and the establishment of standards and certification program for CF

THE INFLUENCE OF USING WORD WALL ON THE STUDENTS’ VOCABULARY MASTERY AT THE SECOND SEMESTER OF THE EIGHTH GRADE OF SMP DWI PANGGA BANDAR LAMPUNGIN 2017/2018 ACADEMIC YEAR

Vocabulary is very important for learners. Learning a language cannot be separated from learning vocabulary because the language itself consists of many vocabularies which make up a language. Knowing a language means knowing the words of that language. It must be impossible to learn English without vocabulary. If the students have lack of vocabulary, they cannot express their ideas, and it is impossible to communicate effectively among people. The objective of the research is to know whether there is significant influence of using word wall on the students’ vocabulary mastery at the second semester of the eighth grade of SMP Dwi Pangga Bandar Lampung in 2017/2018 academic year. The research methodology of this research was quasy experimental design, in this researcher, the population of the research was the eighth grade of SMP Dwi Pangga Bandar Lampung. The sample of this research was two classes consist of 25 students as experimental class and 30 students as control class. In the experimental class. The researcher used wordwall media and cross puzzle in control class. The treatments were held in three meeeting in which 2 x 40 minutes for each class. In collecting the data, the researcher used instrument in the form of multiple choice test which had been tried out before giving the treatment, the instrument was given in pre-test and post-test. Before giving treatment, the researcher gave pre-test and post-test for both of classes. After giving pre-test and post-tes, the resarcher analyzed the data using SPSS to compute independent sample t-test. From the data analysis computed by using SPSS, it was obtained that Sig. = 0,0009 and α =0.05. it means that Ha is accepted because Sig. < α= 0,05 . Therefore there is a significant influence of using wordwall media on the students’ vocabulary mastery at the second semester of the eighth grade of SMP Dwi Pangga Bandar Lampung

PENERAPAN MODEL PEMBELAJARAN QUANTUM LEARNING UNTUK MENINGKATKAN HASIL BELAJAR GEOGRAFI SISWA RNKELAS X-2 SMA NEGERI 1 SAMADUA RNKABUPATEN ACEH SELATAN

ABSTRAKKatakunci :Penerapan, Model Pembelajaran Quantum Learning, Hasil Belajar.Pada proses belajar mengajar guru mengupayakan cara-cara untuk meningkatkan penguasaan materi, tetapi masih ada siswa yang mengalami kendala-kendala dalam proses belajar mengajar tersebut. Model Quantum Learning merupakan salah satu strategi yang digunakan untuk mengoptimalkan proses pembelajaran. Rumusan masalah dalam penelitian adalah Apakah penerapan model pembelajaran Quantum Learning dapat meningkatkan hasil belajar geografi siswa, dan bagaimana keterampilan guru dalam mengelola pembelajaran serta bagaimana respon siswa terhadap model pembelajaran Quantum Learning. Adapun tujuan penelitian ini adalah untuk mengetahui peningkatan hasil belajar geografi siswa dengan penerapan model Quantum Learning, untuk mengetahui aktivitas guru dan siswa dalam kegiatan belajar mengajar, keterampilan guru dalam mengelola pembelajaran, dan respon siswa terhadap model pembelajaran Quantum Learning. Jenis penelitian ini adalah Penelitian Tindakan Kelas. Subjek penelitian ini adalah siswa kelas X-2 SMA Negeri 1 Samadua yang berjumlah 19 orang dan objek penelitian ini adalahpenerapan model pembelajaran Quantum Learning. Teknik pengolahan data menggunakan rumus statistik deskriptif, P=F/Nx100%.Untuk pengumpulan data menggunakan tes dan lembar respon siswa. Hasil analisis data menunjukkan bahawa terdapat peningkatan prestasi setelah menggunakan model pembelajaran Quantum Learning. Hal ini dapat dilihat dari hasil pretest dan postest. Pada siklus I secara klasikal telah tuntas 60%dari10 soalterdapat 6 soal yang tuntas,. Secara individual tuntas sebesar 68,42 % atau dari 19 siswa, hanya 6 orang siswa yang tidak tuntas. Pada siklus II secara klasikal sudah tuntas sebesar 90% dari 10 soal tes hanya 1 soal yang belum tuntas. Secara individual tuntas sebesar 94,73 % atau dari 19 siswa hanya 1 siswa yang belum tuntas. Dapat disimpulkan bahwa pembelajaran model Quantum Learning pada materi Hidrosfer dapat meningkatkan hasil belajar siswa

Hubungan Derajat Merokok dengan Penuaan Kulit berdasarkan Klasifikasi Glogau

Skin aging is a progressive changes in the skin and the skin support systems which begins with structural changes and skin elasticity. Smoking is one of important factor that causes skin aging. The aim of this study was to find out the relationship between the degree of smoking and skin aging based on Glogau classification. This analytical research was conducted in RSUP. Dr. M. Djamil. Padang. Men, age 20-60 years old and active smokers were included by simple random sampling. Brinkman index was used to determine the degree of smoking and Glogau classification to determine the respondents’ severity of skin aging. The data were analyzed by Chi-Square test. The results showed that more than half of respondents were in the age group of 20-30 years (52.1%), most of respondents (56.3%) had a mild degree of smoking, and more than one third (37.5%) had skin aging Glogau type II (moderate). Glogau type I (mild) was most commonly found at the age of group 20 – 30 years (56.0%). Glogau type III (advanced) was most commonly found in respondent who have moderate and severe smoking (25.0%). Chi-Square test analysis showed the p-value =0.003 (p <0.05), which means that there is a significant relationship between the degree of smoking and skin aging based on the classification of Glogau. In conclusion, the degree of smoking has a significant relationship with skin aging severity based on Glogau classification. Keywords: Brinkman index, Glogau classification, Skin aging, Smoking. ABSTRAK HUBUNGAN DERAJAT MEROKOK DENGAN PENUAAN KULIT BERDASARKAN KLASIFIKASI GLOGAU Oleh Nadia Khair Penuaan kulit merupakan perubahan progresif pada kulit dan jaringan dibawahnya yang ditandai dengan adanya perubahan struktural dan elastisitas kulit. Merokok merupakan salah satu faktor penting penyebab penuaan kulit. Penelitian ini dilakukan untuk mengetahui hubungan derajat merokok dengan penuaan kulit berdasarkan klasifikasi Glogau. Penelitian ini dilakukan di RSUP. Dr.M. Djamil Padang. Laki – laki, usia 20 – 60 tahun, dan perokok aktif merupakan kriteria inklusi pada penelitian ini. Pengambilan sampel dilakukan dengan teknik simple random sampling. Kuisioner indeks Brinkman digunakan untuk mengetahui derajat merokok dan klasifikasi Glogau untuk menilai tipe keparahan penuaan kulit responden. Data di analisis menggunakan uji Chi-Square. Hasil penelitian menunjukkan bahwa lebih dari setengah usia responden berada pada kelompok usia 20-30 tahun (52,1%), sebagian besar responden memiliki derajat merokok ringan (56,3%), dan lebih dari sepertiga responden (37,5%) memiliki penuaan kulit Glogau tipe II (sedang). Glogau tipe I (ringan) terbanyak terdapat pada kelompok usia 20-30 tahun (56,0%) berdasarkan kelompok usia. Glogau tipe III (lanjutan) terbanyak terdapat pada responden yang memiliki derajat merokok sedang & berat (25,0%). Analisis bivariat menunjukkan nilai p=0,003 (p<0,05), yang berarti terdapat hubungan yang signifikan antara derajat merokok dengan penuaan kulit berdasarkan klasifikasi Glogau. Dapat disimpulkan, derajat merokok memiliki pengaruh yang bermakna terhadap tipe keparahan penuaan kulit berdasarkan klasifikasi Glogau. Kata kunci : Indeks Brinkman, Klasifikasi Glogau, Merokok, Penuaan kulit

The culpability of accounting practice in promoting bribery and corruption in developing countries

Bribery and corruption are increasing in the developing countries. It has been estimated that some $400 billion of bribe is paid to political elite in developing countries. Such huge amounts of money cannot be successfully executed without the active involvement of multinational companies (MNCs) from the Western countries. This paper examines the processes involved in the misapplication of accounting practice from the perspective of anti-social criminal practices. It analyses the implication of accounting practice in the construction of MNCs bribery and corruption activities. The paper locates MNCs enterprise culture and accounting practice within the broader dynamics of global capitalism to argue that the drive for higher profit at almost any cost is not constrained by accounting rules, laws and even periodic regulatory actions. The paper uses publicly available evidence to illuminate the role of accounting technology in concealing and facilitates MNCs corrupt practices in developing countries. Evidence is provided to show that to secure and retain business in developing countries and to gain competitive advantages MNCs have engaged in bribery and corruption. The paper also makes suggestions for reform