Kinetic studies of neighbouring group participation in organic halides and sulphonates

The effect of anchimeric assistance by neighbouring groups on the rates and products for the solvolysis of organic halides and sulphonates has been widely studied,(^1) but the activation parameters of such internal nucleophilic substitutions (S(_N)i) have received relatively little attention. This thesis describes experiments aimed at obtaining this information for the effect of neighbouring hydroxyl, methoxyl and phenyl groups on reactions with aqueous acetone. Compounds containing these substituents but reacting by the normal bimolecular mechanism (s(_N)2) were also examined, and data(^2) for the unimolecular reactions (S(_N)l) of substrates with structurally similar reaction centres allowed a comparison to be made of the entropies and heat capacities of activation associated with these three mechanisms. The chlorohydrins, HO(CH(_2)(_n)CH(_2)Cl, (I; n = 1-5) showed the enhanced rates and the abnormal reaction products expected for the S(_N)i mechanism when n = 3,4, as previously reported for reaction in water(^3). Entropies and heat capacities of activation for these compounds were intermediate between the values of the parameters for the solvolysis of structurally similar substrates by mechanisms S(_N)l and S(_N). The corresponding methoxy-bromides, MeO(CH(_2))(_n)CH(_2)Br, (II; n = 1-5) showed very similar kinetic features when initial rates were measured, but subsequent reactions of the intermediate produced in the first step of the S(_N)i process (n = 3,4) made it difficult to obtain rate coefficients with sufficient accuracy for the determination of accurate activation parameters. Similar results had already been reported for the reactions of MeO(CH(_2))(_2)CH(_2)0Bs, (III; n = 1-5) but approximate rate coefficients could be assigned to the individual reaction steps in the present work. Anchimeric assistance by a phenyl group in the reactions of C(_6)H(_5))(_3)CCH(_2)Cl and (C(_6)H(_5))(_3)CCH(_2)OTs was accompanied by more positive activation parameters than in similar S(_N)l and 5(_N)2 reactions. The results allowed some estimate to be made of the effect of individual leaving groups on the values of the entropies and heat capacities of activation for reaction by mechanism S(_N)i

The Role of the School Psychologist in the Teaching of Reading

The school psychologist or psychological examiner without specific training in the reading area can help the teacher of reading to better understand her task. The psychologist or examiner with background in the teaching of reading can be of even more help to the classroom teacher

KREATIVITAS GURU DALAM PENGEMBANGAN MEDIA PEMBELAJARAN DI TAMAN-KANAK-KANAK

Teachers are required to be creative in developing learning media by utilizing surrounding natural materials so that they can reduce costs. Each region has tremendous natural potential and can be used for the development of learning media in early childhood education. Such as: plants, wood shavings, wood waste from furniture, shells, and other natural materials. The creativity of teachers is required so that the learning process can be fun and varied so that children do not feel bored, with the variety of media used in early childhood learning, learning objectives can be achieved. Given the limited operational costs of TK/PAud educational institutions that cause the lack of media used in learning, the use of natural materials can be a solution in developing learning media that are cheap and easy to obtain from the surrounding environment but still prioritize aspects of security, comfort.Keywords: Teacher Creativity, Learning MediaTeachers are required to be creative in developing learning media by utilizing surrounding natural materials so that they can reduce costs. Each region has tremendous natural potential and can be used for the development of learning media in early childhood education. Such as: plants, wood shavings, wood waste from furniture, shells, and other natural materials. The creativity of teachers is required so that the learning process can be fun and varied so that children do not feel bored, with the variety of media used in early childhood learning, learning objectives can be achieved. Given the limited operational costs of TK/PAud educational institutions that cause the lack of media used in learning, the use of natural materials can be a solution in developing learning media that are cheap and easy to obtain from the surrounding environment but still prioritize aspects of security, comfort, convenience, friendliness. environment and fun for children.Keywords: Teacher Creativity, Learning Medi

PENINGKATAN KREATIVITAS MENGGAMBAR DENGAN MENGGUNAKAN MEDIA PASIR DI TK NEGERI PEMBINA I KECAMATAN DATUK BANDAR KOTA TANJUNGBALAI

Penelitian ini bertujuan untuk mengetahui peningkatan kreativitas meng gambar anak dengan menggunakan media pasir.Perumusan masalah penelitian yang dilakukan yaitu apakah dengan menggunakan media pasir dapat meningkat kan kreativitas menggambar dan bagaimana proses pembelajaran dengan menggu nakan media pasir dapat meningkatkan kreativitas menggambar. Tujuan peneliti an yaitu untuk meningkatkan kreativitas anak melalui menggambar dengan meng gunakan media pasir,mendiskripsikan aktivitas menggambar dengan mengguna kan media pasir.Subjek penelitian ini adalah TK Negeri Pembina I Kecamatan Datuk Bandar Tanjungbalai yang berjumlah 19 orang yang terdiri dari 10 anak la ki-laki dan  9 anak perempuan. Teknik pengumpulan data dilakukan dengan observasi, percakapan,hasil karya,dokumentasi.Analisis pengumpulan data dilaku kan dengan teknik hasil data dan catatan lapangan dan penarikan kesimpulan. Hasil penelitian dapat disimpulkan bahwa dalam siklus kedua terjadi peningkatan pembelajaran menggambar.Pada siklus satu menggambar dengan menggunakan media pasir mencapai ketuntasan 63%.Sedangkan pada siklus kedua kreativitas menggambar dengan media pasir meningkat dengan mencapai 83%.Berdasarkan hasil penelitian dapat disimpulkan bahwa dengan media pasir dapat meningkat kan kreativitas menggambar ana

158µJ pulses from a single transverse mode, large mode-area EDFA

We report the amplification of 10pJ-100pJ, semiconductor diode pulses up to an energy of 158µJ and peak powers >100kW in a multi-stage fibre amplifier chain based on a single-mode, large mode-area erbium doped amplifier design. These results represent the highest single-mode pulse energy ever extracted from any doped fibre system

Linearisation Method of DML-Based Transmitters for Optical Communications Part III: Pulse Amplitude Modulation

A new linearization method for optical transmitters based on directly modulated lasers (DMLs), named the Stretched A method, was proposed in Parts I and II of this work. Parts I and II presented the theoretical framework of the method for non-return-To-zero (NRZ) modulation and related detailed simulation and experimental results. Here, we extend the method to pulse amplitude modulation schemes (PAM). Focussing on 4-level PAM (PAM-4), we present the theoretical background and discuss implementation options. A simplified variation of the method for the generation of PAM signals with a significantly lower number of sub-currents is proposed. Simulation studies for PAM-4 transmission at 50 GBaud (100 Gb/s) and an experimental proof-of-principle demonstration at 16 GBaud (32 Gb/s) are reported based on 850 nm vertical-cavity surface-emitting lasers (VCSELs). For PAM-4, products of effective eye diagram areas ({\boldsymbol{PS}}) of 0.6 × 10-5 and 43 × 10-5 before and after applying the Stretched A method were measured, demonstrating an improvement ratio of ∼72. The sensitivity and tolerances of the method are analyzed using simulation and experiment

Linearisation Method of DML-based Transmitters for Optical Communications Part II: Experimental Demonstration and Implementation Methods

In this paper, we report the first experimental demonstration of the Stretched A linearisation method. The theoretical framework of the method and related simulation studies have been presented in Part I of this work. Here, we apply the method on an 850 nm multimode vertical-cavity surface-emitting laser (VCSEL) specified for operation at 10 Gb/s and demonstrate good quality optical output waveforms with little non-linear distortion at 16 Gb/s using non-return-to-zero (NRZ) modulation. An experimental sensitivity analysis on the generation of the required modulating current components demonstrates large tolerance to parameter mismatch. In addition, it is shown that an adaptive gain scheme can improve the tolerance to the timing offset between the current components. Potential hardware implementations using either analog or digital electronics are also discussed