Electronic Spectra of Aromatic Hydrocarbons: A Deductive Approach to the Diffuse Interstellar Bands

The diffuse interstellar bands (DIBs) are a series of more than 500 interstellar absorption features, the carriers of which have remained unidentified since 1919. In order to determine which aromatic chemical species are likely to be carriers of the DIBs, trends observed in the spectroscopic features of polycyclic aromatic hydrocarbon (PAH) species with chromophores ranging from 6 to 17 carbon atoms are considered. These trends are explored for PAHs with differing charge states and multiplicities, for multiple electronic transitions. Previously unreported electronic transitions of the neutral radicals 1-naphthylmethyl, 2-napthylmethyl, 9-methylanthracene and 1-pyrenylmethyl as well as the 9-methylanthracenium+ and phenalenium+ radical cations and the closed-shell neutral molecule 1H-phenalene were recorded. The D1 ← D0 transitions of small PAH resonance stabilized radicals (RSRs) are shown to be unlikely to be responsible for the DIBs. The spectroscopic properties of larger PAH RSRs were empirically extrapolated from experimental and computational trends. The vibronic structures of these molecules were assigned. As the D1 ← D0 transitions of PAH RSRs are weak, techniques were developed to obtain the gas-phase spectra of more intense electronic transitions to higher excited-states by double-resonance spectroscopy. Several strong transitions were observed, which were then assigned using ab-initio and TD-DFT computational methods. The spectra of PAH radical cations were recorded. The recorded spectra covered a range from the mid infrared to the ultraviolet. As a result of the work presented, several classes of PAH can now be dismissed as possible carriers of the DIBs. Further avenues of research have been suggested. The role of this work as part of the ongoing search for the carriers of the DIBs will be discussed

Metrology and Transport of Multiply Charged Ions

The transport and interaction of singly- and multiply-charged ions with matter has been studied. The experiments were performed in an ultra-high vacuum environment. The low- and hyperthermal-energy ion beamline was used as a source of singly charged ions, while the CUEBIT facility was used as a source of multiply charged ions. The kinetic energy of the ion beam obtained from the CUEBIT is offset from the nominal value expected from the applied electrostatic potentials. These offsets were studied by measuring the kinetic energy of the beam using a retarding field analyzer (RFA). The offset was attributed to the space charge of the electron beam that is used to create the multiply charged ions. The charge density of the electron beam was varied by changing operational parameters of the electron beam, namely the electron beam current and the energy of the electron beam. Ion beams of Ar4+ and Ar8+ were extracted from the source and the offsets observed in the kinetic energy were related to the variation in the space charge potential of the electron beam. Measurements of these offsets, ranging from 100 eV/Q to 300 eV/Q, are significant and important for experiments that aim to utilize the potential energy of slow multiply charged ions. The transport of ions using capillaries has been studied to investigate the viability of ion-guiding as a means for a novel ion delivery mechanism. Results on transport through large bore capillaries (macrocapillaries) that probe both the geometric and ionguided mechanisms are presented. The angle- and position-dependent transport properties were found to depend on the material of the capillary (specifically, whether metal or insulator) and the geometry of the capillary. Rb+ ions at a kinetic energy of 1 keV were transmitted through metal and glass capillaries that were a few centimeters in length and a few millimeters in diameter. Oscillations were observed in the capillaries made of glass which were absent in the metal capillaries. Calculations based on the geometry of the experimental setup and kinematics of the ions showed that these oscillations could be attributed to the charge patches formed on the capillary walls. Electronic excitations in solids due to energetic ions at low kinetic energy were measured by using Schottky diodes. Hot electron currents measured at the backside of an Ag/n-Si Schottky diode due to ion bombardment on the frontside were found to depend on the kinetic energy (500 eV to 1500 eV) and angle of incidence (+/-30o) of the ion (Rb+) beam. A sharp upturn in the energy dependent yield is consistent with a kinetic emission model for electronic excitations utilizing the device Schottky barrier as determined from current-voltage characteristics. Backside currents measured for ion incident angle are strongly peaked about normal incidence. Accounting for the increased transport distance for excited charges at non-normal incidence, the mean free path for electrons in silver was found to be 5:2 +/- 1:4 nm, which is consistent with values reported in the literature

Seattle Pacific University Catalog 1997-1998

https://digitalcommons.spu.edu/archives_catalogs/1079/thumbnail.jp

Critical Thinking Skills Profile of High School Students In Learning Science-Physics

This study aims to describe Critical Thinking Skills high school students in the city of Makassar. To achieve this goal, the researchers conducted an analysis of student test results of 200 people scattered in six schools in the city of Makassar. The results of the quantitative descriptive analysis of the data found that the average value of students doing the interpretation, analysis, and inference in a row by 1.53, 1.15, and 1.52. This value is still very low when compared with the maximum value that may be obtained by students, that is equal to 10.00. This shows that the critical thinking skills of high school students are still very low. One fact Competency Standards science subjects-Physics is demonstrating the ability to think logically, critically, and creatively with the guidance of teachers and demonstrate the ability to solve simple problems in daily life. In fact, according to Michael Scriven stated that the main task of education is to train students and or students to think critically because of the demands of work in the global economy, the survival of a democratic and personal decisions and decisions in an increasingly complex society needs people who can think well and make judgments good. Therefore, the need for teachers in the learning device scenario such as: driving question or problem, authentic Investigation: Science Processes

Pengembangan Bahan Ajar Cai Ipa Dengan Pendekatan Integrative Learning Untuk Meningkatkan Hasil Belajar Siswa

Abstrak Pada era globalisasi kemajuan teknologi komunikasi dan informasi berkembang begitu pesat, hal ini membawa perubahan pada setiap aspek kehidupan, termasuk pada sistem pendidikan dan pembelajaran. Sehingga diperlukan terobosan dan inovasi baru dalam proses pembelajaran yang dilakukan guru dengan memanfaatkan multimedia dalam menyampaikan materi ajar. Salah satu bahan ajar multimedia tersebut adalah Computer Assisted Instuction (CAI). Penelitian ini bertujuan untuk mengembangkan bahan ajar CAI dengan pendekatan Integrative Learning untuk meningkatkan hasil belajar IPA. Jenis penelitiannya adalah penelitian dan pengembangan yang dikembangkan oleh Sukmadinata. Tahapannya meliputi; 1) Studi Pendahuluan, 2) Pengembangan Produk, dan 3) Uji Produk. Data kualitatif diambil dari instrumen yang diberikan oleh ahli materi, ahli media, dan keterbacaan bahan ajar oleh siswa, sedangkan data kuantitatif adalah hasil tes belajar siswa sebanyak 72 siswa. Analisis data menggunakan uji t dan melihat dampaknya menggunakan effect size. Hasil penelitian menunjukkan bahwa produk bahan ajar CAI IPA ini sangat layak untuk digunakan dalam pembelajaran di SMP dengan capaian nilai validator materi 3,81, capaian nilai validator media 3,65, dan dari siswa 3,31. Uji efektivitas produk pengembangan bahan ajar CAI IPA dilihat dari nilai rerata kelas eksperimen 75,42, sedangan nilai rerata kelas kontrol 60,54. Setelah dilakukan Uji t taraf signifikansi 0,05 diperoleh �ℎ����� 5,794 > ������ 1,99, disimpulkan bahwa terdapat perbedaan secara signifikan hasil belajar siswa yang menggunaan bahan ajar CAI IPA dibandingkan dengan hasil belajar siswa secara konvensional. Kekuatan penelitian ini adalah bahan ajar CAI IPA yang dikembangkan lebih effektif dan effisien, dalam waktu yang sama, siswa akan belajar lebih cepat, menguasai materi dan mengingat lebih banyak dari apa yang sudah dipelajari. Kelemahannya adalah diperlukan dukungan software dan hardware yang memadai untuk menggunakannya. Kata Kunci: CAI, Integrative Learnin