Question Exercise 1.2 Consider these documents:. Doc 1 breakthrough drug for schizophrenia. Doc 2 new schizophrenia drug. Doc 3 new approach for treatment of schizophrenia. Doc 4 new hopes for schizophrenia patients a. Draw the term-document incidence matrix for this document collection b. Draw the inverted index representation for this collection, as in Figure 1.3 (page 7) Answer a.
Doc 1 Doc 2 Doc 3 Doc 4 Breakthrougt 1 0 0 0 Drug 1 1 0 0 For 1 0 1 1 Schizophenia 1 1 1 1 New 0 1 1 1 Approach 0 0 1 0 Treatment 0 0 1 0 Of 0 0 1 0 Hopes 0 0 0 1 Patients 0 0 0 1 b. Question Exercise 1.7 Recommend a query processing order for d. (tangerine OR trees) AND (marmalade OR skies) AND (kaleidoscope OR eyes) given the following postings list sizes: Term Posting Size Eyes 213312 Kaleidoscope 87009 Marmalade 107913 Skies 271658 Tangerine 46653 Trees 316812 Answer tangerine OR trees – tangerine tangerine OR trees marmalade OR skies – marmalade marmalade OR skies kaleidoscope OR eyes – kaleidoscope kaleidoscope OR eyes – trees AND skies AND eyes Question Exercise 1.10 Querstion Gunakan google dan yahoo. Coba beberapa query boolean.
Feb 03, 2016 Cara Membuat Aplikasi Program sederhana Menggunakan Microsoft Foxpro andika skin. Cara Membuat Undangan Berbingkai dengan MSWord. Tutorial Makeup Simple Ga Pakai Lama (pacar tidak.
Catat hasil yang diberikan. Answer query boolean – harry potter AND twilight query boolean – harry potter OR twilight.
Manajemen proyek web sangat berbeda dari maanjemen proyek perangkat lunak tradisional. Manajemen proyek adalah aktifitas manusia untuk membentuk tindakan dari manusia lainnya. Apa arti sebuah proyek? Proyek adalah sebuah usaha yang menghasilkan seperangkat pengiriman dalam waktu tertentu, biaya dan kualitas tertentu. Suatu proyek akan mempunyai ciri-ciri sebagai berikut:.
Unik secara alami Proyek tidak melibatkan proses pengulangan. Mempunyai batasan waktu Proyek mempunyai permulaan yang jelas dan tanggal akhir dengan pengiriman yang harus dihasilkan untuk memenuhi keperluan pelanggan. Mempunyai anggran yang telah disetujui Proyek adalah tingkat yang telah dialokasikan dari pengeluaran keuangan dengan pengiriman yang telah dihasilkan untuk memenuhi keperluan pelanggan tertentu. Mempunyai sumber yang terbatas Pada awal pekerjaan proyak telah disetujui, peralatan dan material telah dialoksikan ke proyek. Meliputi elemen resiko Proyek yang mengakibatkan ketidakpastian akan mengakibatkan resiko bisnis. Mendapatkan perubahan keuntungan Tujuan dari sebuah proyek secara umum adalah untuk mengembangkan sebuah perusahaan melalui penerapan perubahan bisnis Apa itu manajemen proyek?
Manajemen proyek adalah suatu keahlian, peralatan, dan proses manajemen yang diperlukan untuk kesuksesan sebuah proyek. Web muncul sebagai suatu sistem hypertext yang sangat sederhana yang mendukung konsep global. XML merupakan teknologi hypertext yang pertama. Web banyak dikoneksikan dengan database untuk membuat suatu system informasi. Integrasi modul perangkat lunak yang luas diklien dan server dan teknik design berorientasi objek merupakan hal yang penting dalam “Melting pot Web”. Namun, ketiga aspek tersebut yang disebutkan tetap signifikan, tidak satupun dari tiga aspek diatas dapat menawarkan solusi yang memuaskan.
Menurut Evolusioner salah satu karakteristik utama aplikasi Web adalah dokumen-terpusat, yaitu, bagaiman orang dapat membaca dan mengerti apa isi yang dimaksud. Isi adalah raja. Awalnya, Tim Berners-Lee ingin mengembangkan Web menjadi sederhana meskipun sistem hypertext di seluruh dunia melalui Internet, berfokus pada informasi tekstual. Design Informasi: Aktifitas Autorasi Bagian ini membedakan antara era sebelum Web, era HTML (dari kedatangan Web sampai 1997), dan era XML saat ini (W3C 1998). Awal era HTML secara eksklusif terfokus pada authoring. Hanya dokumen hypertext yang didukung, dari namanya HTML(Hypertext Markup Language) pada HTML, seluruh dokumen teks akan dipenuhi oleh tag-tag dari HTML.
Dalam perkembangannya, HTML pun mendukung media lain, seperti: gambar, Video, Audio dan lain-lain. Programmable Web HTML berkembang menjadi dinamis, kedinamisan ini menggunakan script, sehingga dapat disesuaikan dengan kebutuhan dari browser maupun server. Dengan script ini maka dokument HTML akan menjadi dinamis, seperti adanya efek pada dokumen. Para pengembang Java memperkenalkan “Bahasa Web baru” dengan dasar bahwa setiap browser tidak hanya terdiri dari HTML, tetapi juga aplikasi java. Bahasa ini serupa dengan dokumen HTML, tetapi terdiri dari Java Applet yang didownload dari server, dan bukan dokumen statis, setelah itu suatu tampilan akan tampil di browser setelah proses download selesai.
Dokumen HTML disebarkan melalui internet yang menggunakan koneksi TCP, inter-process communication (IPC) Masalah dan Pembatasan dalam Desain Web Terpadu Jalan menuju integrasi hypertext, informasi, dan desain perangkat lunak ke dalam desain web adalah bergelombang, terutama disebabkan oleh tiga kendala spesifik: yakni budaya, teknologi, dan masalah konseptual. Pendekatan Struktural Daftar Tiga bagian pada sisi komponen dan sisi Mesh, yaitu: 1. Desain Presentasi: pada desain ini memiliki output dokumen, media, dan data (dalam arti sistem informasi, atau dalam arti Komponen data aplikasi perangkat lunak). Di sisi mesh, desain ini harus fokus pada visualisasi, auditori atau output multi-modal dari mesh, dan komponen yang dikunjungi oleh pengguna.
Desain Interaksi: pada bagian ini berkaitan dengan aliran kontrol interaksi pengguna dengan aplikasi Web. Di sisi mesh, istilah navigasi sudah menjadi kebiasaan, sementara istilah dialog digunakan pada sisi komponen. Desain Fungsional: desain inti dari komponen dan mesh, menekankan perspektif pengembang perangkat lunak, karena ini penting untuk kategori aplikasi Web terbaru.
Oleh karena itu, sisi komponen akan digambarkan sebagai desain informasi. Demikian pula, sisi mesh akan berfokus pada komposisi komponen aktif dalam proses bisnis(Alur kerja) dan sangat disesuaikan dengan aplikasi web. Desain Presentasi. Dalam desain presentasi, “media desainer” menentukan tampilan dan struktur bagaimana isi multimedia disajikan. Berdasarkan gagasan asli bahwa konten adalah raja, isi HTML klasik ditentukan bersama-sama dengan instruksi format, link, dan sebuah program (script).
Sebaliknya, desain presentasi modern mengikuti konsep pemisahan antara isi aplikasi dan presentasi. Desain presentasi yang baik memungkinkan kita untuk menyesuaikan presentasi dengan kebutuhan budaya, teknologi, dan berbagai kontekstual. Selain itu, banyak halaman Web, aplikasi Web dan situs Web yang direstrukturisasi dengan desain visual baru.
Dalam pengembangan web tradisional ini berarti bahwa ratusan atau bahkan ribuan dokumen HTML harus disesuaikan secara manual. Orang-orang yang terlibat dalam proses modifikasi dokumen HTML biasanya membutuhkan banyak pengetahuan mengenai HTML. Hal ini mengakibatkan biaya yang dikeluarkan cukup besar dan membutuhkan Tim pengembang yang banyak pula. Desain Interaksi Desain Interaksi menyangkut persimpangan visual, dinamis, fungsional, dan teknis dari unsur-unsur aplikasi Web. Tujuan utamanya adalah untuk menggabungkan unsur-unsur tersebut, dalam rangka untuk menarik pengguna dan agar aplikasi mudah dipahami. Bagian ini menunjukkan pendekatan sistematis yang membagi interaksi aplikasi Web menjadi empat aspek: interaksi pengguna, antarmuka pengguna, navigasi, dan aktivitas pengguna. Kriteria User Interface yang harus diperhatikan dalam pengembangan aplikasi Web/perangkat lunak adalah: maintainability, reusability, scalability, sustainability and expandability.
Maintainability mengacu pada upaya untuk mencari dan memperbaiki kegagalan perangkat lunak, dan biasanya diukur oleh kesederhanaan, keringkasan, dan modularitas. Web aplikasi yang menarik menyediakan user interface yang interaktif yang biasanya menggunakan teknologi Active X/ Applet atau AJAX (Asynchronous JavaScript and XML).
User interface ini biasanya memiliki presentasi, data dan logika yang erat, sehingga ada kesulitan dalam pembangunan dan pemeliharaan. Reusability mengacu pada kemungkinan kode aplikasi untuk digunakan kembali tanpa adanya perubahan yang berarti. Kebutuhan untuk mencari reusabilitas di tingkat user interface biasanya sering diabaikan oleh banyak orang. Skalabilitas tidak hanya merujuk pada kemampuan mempertahankan sejumlah besar pengguna tetapi juga dari sudut pandang pembangunan, dengan kemampuan pembangunan yang dapat dilakukan secara paralel oleh tim pengembang. Beberapa teknologi berbasis ActiveX mengaktifkan fungsi yang menakjubkan.
Desain Fungsional Rancangan fungsional juga harus mempertimbangkan aspek-aspek teknologi yang memiliki dampak yang kuat pada aplikasi Web dalam pengembangan. Kita harus mengamati commensurability, tapi aplikasi kita harus diperluas, terukur, dan dipelihara. Kesulitan khusus terlihat dalam interaksi komponen.
Web aplikasi seperti tickers berita biasanya dapat melakukannya tanpa dukungan transaksi, sementara toko-toko online mungkin harus memetakan banyak fase produk. Ini membutuhkan Transaksi dan alur kerja dukungan dan integrasi database dan sistem perangkat lunak. Kesimpulan Web dimulai sebagai suatu infrastruktur hiperteks yang fleksibel berdasarkan pada konsep SGML. Konsep SGML menggunakan teknologi yang sederhana dan menyatukan teknologi lain yang seperti Gopher, FTP, Telnet dan Usenet (NNTP).
Perkembangan Teknologi Kemudian Mengubah Infrastruktur Dokumen Hiperteks menjadi suatu antar muka perangkat lunak yang bisa diremote. Campuran dari dokumen dan tugas memperkenalkan isu baru di dalam antarmuka pengguna seperti organisasi nya, interaksi pengguna, dan faktor-faktor navigasi yang harus ditujukan untuk membangun aplikasi yang sukses. Perkembangan juga terjadi pada Web Browser, dimana setiap web browser mempunyai adaptasi yang berbeda dan cara transcoding yang berbeda pula. Begitupun juga pada Tampilan yang digunakan. Seiring hal itu Perusahaan-Perusahaan yang bergerak dalam bidang aplikasi web pun banyak yang bermunculan.
Bersamaan dengan perkembangan teknologi, perhatian tentang kelemahan kemampuan hiperteks yang asli untuk menghubungkan informasi secara semantis dimunculkan. Semantic Web adalah satu usaha yang berkelanjutan untuk menunjuk hal ini. Bersamaan dengan hal itu, muncul teknologi-teknologi baru yang dipersiapkan untuk memungkinkan Web menjadi suatu sumber Proaktif dan berpengetahuan lebih. Middleware adalah teknologi untuk menghubungkan aplikasi. Pendekatan yang ada sangat berbeda dalam kompleksitas dan tujuan. Di mana kita secara singkat dijelaskan Antar-Proses Komunikasi (IPC), Remote Procedure Call (RPC), Event-Berbasis Komunikasi (EBC), Message-Oriented Middleware (MOM), dan didistribusikan pendekatan berorientasi objek. SOAP menangani pesan dan panggilan melalui Internet protokol yang berbeda, misalnya, HTTP, SMTP, dll WSDL berfungsi untuk menggambarkan antarmuka dan Teknologi 106-aware Aplikasi Web Design alamat layanan Web, dan UDDI menyediakan semacam database untuk mempublikasikan dan mencari Web Context-aware Applications adalah sebuah aplikasi yang membutuhkan pengetahuan khusus pengguna – pengguna konteks – untuk menyesuaikan secara optimal baik interaksi dan fungsinya.
Sejumlah masalah harus dipecahkan untuk dapat luas memperkenalkan jenis aplikasi canggih. Masalah-masalah ini tidak hanya bersifat teknis, misalnya, sehubungan dengan membuat informasi dan konteks yang diperlukan tersedia.
Operator Telecom telah mulai hanya ragu-ragu untuk menyediakan pihak ketiga dengan langkah-langkah teknis dan antarmuka untuk LBS, dan mereka biasanya meminta tingginya harga. Mengingat potensi penjualan besar, operator telekomunikasi tampaknya tertarik menawarkan layanan konteks-sadar sendiri atau melalui mitra yang dipilih. Kurangnya kompetisi dan, akibatnya, rendahnya kualitas layanan yang saat ini ditawarkan membuat model bisnis ini muncul diragukan.
Lain hambatan utama untuk pengenalan aplikasi Web konteks-sadar adalah bahwa pengguna ingin kerahasiaan. LBSs khususnya telah dibahas oleh berdebat apakah atau tidak ketiga pihak dapat merekonstruksi dan penyalahgunaan lokasi pengguna. Manfaat dari Web konteks-sadar aplikasi serta kepercayaan yang tumbuh dan keamanan teknis yang lebih baik akan membantu mengatasi kendala tersebut dalam jangka menengah. Clear kemajuan yang telah diamati dalam dukungan teknis untuk aplikasi Web konteks-sadar. Bagaimana memanggil perintah eksternal Linux dari dalam skrip shell? Perintah eksternal adalah perintah yang bukan bagian internal dari shell (dapat berupa utilitas atau program aplikasi). Semua perintah shell dieksekusi dengan sintaks yang sama: perintah argumen1 argumen2 argumenN Perintah eksternal bisa dieksekusi ketika program masuk didalam pencarian path oleh shell.
Jika tidak, Anda harus menentukan path ke program. Pencarian path dari shell disimpan pada variabel bernama PATH. Sebuah varibel adalah bagian dari memory, dimana nilainya bisa diganti.
Kita bisa melihat isi dari variabel PATH dengan cara berikut: $ echo $PATH /usr/kerberos/bin:/usr/local/bin:/usr/bin:/bin:/usr/X11R6/bin:/home/daniel/bin Untuk Memanggil Perintah eksternal Linux dari dalam ShellBash bisa langsung dipanggil saja(ditulis langsung). Contoh: #!/bin/bash ls #memanggil perintah list 2. Bagaimana cara mengetahui perintah apa saja yang disediakan oleh Linux?
Untuk mengetahui perintah apa saja yang disediakan oleh linux bisa dengan menekan tombol escape (esc) pada keyboard sebanyak 3 kali. Maka akan muncul konfirmasi sebagai berikut (Contoh): adminlab@adminlab-desktop:/Modul2$ Display all 2700 possibilities? Tekan y untuk melihat, maka akan tampil perintah-perintah yang ada. Bagaimana kita dapat mengetahui suatu perintah termasuk perintah Linux atau bawaan shellBash? Jika perintah tersebut ada pada direktori bin maka kemungkinan besar itu merupakan perintah linux, tapi kalau tidak ada maka kemungkinan besar itu merupakan perintah bawaan dari ShellBash. A noise is an unwanted signal and is transmitted along with the original signal over the transmission media. These signals are introduced/generated due to many atmospheric conditions, thunderstorms, rains, etc., and the equipment being used in the communica- tion systems.
There are a variety of noises that have been defined. Next, we discuss types of noises, the sources of the noises, and how these noises can be reduced in communication systems. Electrical noise: This category of noise is basically a high-voltage generator, high-fre- quency unwanted interference on the link. The sources of this noise are transmission stations, lightning, heavy motors and generators, heating and cooling systems, etc.
The high-frequency noise may cause the transmission of signals to wither over the links. In other words, the interference may be between the ground and the lines or between the lines themselves. This noise has a very significant effect on the quality of signal received if we use the frequency modulation scheme in the transmission.
Cros s talk: In an open wire, one wire may pick up the signal transmission on an adjacent wire and thus cause interference in it. We experience this problem when we notice that our voice is not clear or we get many other voices together while using the telephone system. The interference created by open wires is called cross talk. Here the electromagnetic waves of the signals flowing through adjacent wires interfere with each other due to the inductive and capacitive effects created by other circuits near these lines, e.g., power lines, telephone lines, and other interference facilities. Cross talk may also be created by motors, generators, or even transmitters/receivers near the lines.
This type of noise (distortion) is very common with open wire systems because telephone companies link the pairs of open wires as a carrier system using amplifiers accommodating 12 voice-grade channels using FDM. When we use a parallel pair of wires (or cables), current flowing in each wire either in the same direction or in opposite directions will interfere with each other. This is due to the fact that the electromagnetic fields induced by the flow of current will interfere with each other, affecting the value of current and hence the quality of signals. In real life, sometimes we notice this type of noise (due to some other conversation) while using a phone. Either twisting the wires or putting a separator between parallel wires can mini- mize this noise, which reduces the interference effect between the electromagnetic fields. Impulse noise (spikes): We know that the electrons constituting the current flowing in a metallic wire have a random movement and sometimes, due to this random movement. Neighboring components of the electronic circuits experience thermal energy which causes the thermal motion of the electrons in the electronic circuit.
This is caused due to the sudden increase in the amplitude of the signal to peak value within or outside the data communication circuit. The peak value of the amplitude of the noise (or internal impulse noise) is usually caused by poor connections and contacts, loose connections, improper grounding, etc., and can be noticed in the telephone system where we sometimes do not hear any tone.
The external impulse noise is typically caused by atmospheric conditions such as thunderstorms, lightning, or even relay switchgear near the station. One can feel this noise in an AM receiver during bad weather, thunderstorms, or even rains. This noise is a form of random impairment. We notice this type of noise (hum) when we turn off our radio or when it is not tuned to any station at a moderate volume. At low volume, we may not notice it, but if the volume is moderate, we will hear this noise.
This noise has different names, such as white noise, Gaussian noise, random noise, etc. The most common name for this noise is Gaussian (random) as its amplitude follows the very popular Gaussian distribution func- tion. The name white noise is derived from the fact that this noise occurs at all frequencies in more or less the same way. It is also known as thermal noise because the noise level varies linearly with the temperature of the system.
This is due to the thermal agitation of electrons; this type of noise cannot be reduced and is independent of distance. T ransient noise: This is another form of random impairment noise and is usually caused by sudden voltage change (due to power equipment or heavy transformers), electrical storms, and even rotary motion during the dialing of rotary telephone systems, etc. Some people consider both noises (transient and impulse) the same and, as a matter of fact, this may be true, as some sources for these noises are common. The duration of transient noise may vary from a few milliseconds to a few seconds and depends on the magnitude of voltage developed by the sources. The loss of bits from bit rate transmission depends on the duration of transient noise. Shielding the wires may reduce this noise.
Phase jitter: This noise is usually caused by interfering with the phase shift of a trans- mitted signal and can be noticed at the receiver side. It has been shown that this noise is of the form of frequency or phase modulation and seems to have little effect on the transmission of voice-grade channel. It becomes one of the significant performance criteria for data communication as it limits the speed of the transmission. It usually causes errors in the data stream, which are transmitted over a frequency-division-multiplexed commu- nication channel. In the single-sided-band amplitude modulation (SSB-AM), the carrier frequency is changed to a higher level (based on the amplitude of modulating signal) before multiplexing at the transmitting side, while the carrier frequency is changed to a lower value after de-multiplexing at the receiving side (to recover the original level).
The carrier frequency must be the same at both ends (transmitter and receiver) of the commu- nication link. Phase jitter will occur if the carrier frequency at the ends is not same. This difference of carrier frequency between two sides may be due to many factors such as ripple voltage noises in the respective oscillator circuits. Phase jitter is usually measured as peak-to-peak derivation of the instantaneous value of the phase angle of the signal. In voice telephone communication, it may affect only the quality of voice received, but in the case of data communication, the loss of a large number of bits in a bit rate transmission becomes a serious problem. This noise may be reduced by using highly stable frequency circuits, multiplexers of the required specifications, etc.
In most of the data and voice communications, the self-test tones may be transmitted to the receiver to measure the phase jitter between them and the received signals can be calibrated accordingly. This noise cannot be reduced and is independent of distance. Harmonics distortion: This distortion is generated by different circuits (amplifiers, mod- ulators, etc.) of communication systems and is defined as unwanted signals having integer multiples of amplitude frequencies of the original signal.
The output of these circuits, in general, does not have a linear relationship with the input. The functions of the circuits provide nonlinear distortions and are collectively known as harmonic distortions. Using linearizing circuits to eliminate the effect of nonlinearity on the output transmitted signal may reduce this noise. Othe r noises: Lightning storms and faulty equipment cause catastrophic noise that cannot be reduced, and it increases with distance. The higher-frequency signals lose their strength more than lower-frequency signals, which causes attenuation errors.
Amplitude errors are caused by a sudden drop in power caused by faulty electrical connection or contacts, change in load, or switching errors. Errors which occur in burst are known as bursty errors.
Inter- modulation noise is similar to cross talk and is created by modems due to the interference between two signals. For more details on noise and other distortions, see Reference 4. Echoes: This noise can be noticed during a conversation on a telephone system.
The two- wire lines are connected to the network (typically four-wire lines) and the impedance of both two-wire and four-wire lines varies with the frequency in the communication circuits. Impedance is a generic word used to represent the effect of various components (induc- tance, capacitance, and resistance) with reference to frequency in the communication circuit.
In addition to this, there may be a mismatch of impedance between two-wire and four-wire lines. The total effect of these causes is noticed by getting a portion of the signal reflected back to the source in the form of an undesirable signal, which is called an echo. Echoes on data lines cause intermittent errors. A speaker may get an echo of his/her own voice if there is a mismatch at the trans- mission side. This may have a significant effect on the conversation. If a delay of the signal (going from the microphone to the junction and coming back) is small, the speaker ’s voice can be heard in his own receiver. If the delay is substantial, it has a significant effect on the receiver because the speaker has to repeat the conversation, speak louder, etc., causing dissatisfaction.
This type of echo has little effect on the listener ’s side if the delay is small, but if it is large, the listener is unable to understand the conversation because it sounds like more than one person is talking simultaneously. Fortunately, this noise has little effect on data communication when we are using half duplex. For short-distance communica- tions, echoes are generally tolerable, but for long-distance communication, impedance mismatching becomes a serious problem and echo suppressers, echo-cancellation tech- niques, etc., must be used.
The echo suppressor device reduces the problems of echoes caused by mismatching by comparing the transmitted and received paths for the signals. If the difference in the levels of signals over the paths is significant, it adjusts the signal levels over the paths to the levels by which the effect can be neutralized or reduced. It operates over four-wire lines, as shown in Figure 2.7(a). PADs define the adjustment of levels. When the node is transmitting signals over the transmitting path and the signal level on this path is much higher than the receiving path, the echo suppressor switches the PADs onto the the receiving path to reduce the effect of echo loss, as shown in Figure 2.7(b).
In the case where the node is in transmitting mode, it inserts the losses in the trans- mitting path so that we do not get any loss on the receiving path. The echo suppressor circuit must include minimal round-trip propagation delay in the telephone system; oth- erwise, the quality of the voice signal will be affected considerably. The echo suppressors used for the telephone system usually do not work on the tone frequencies (2000-2250 Hz), but once the connection is made, the signals can be transmitted over the link. T ransmission distortion: These distortions are caused because transmitted signals take different times to reach the receivers. For example, in radio frequency (RF) transmission in the range of 3–30 MHz, the transmitted signals may be affected by magnetic storms, cosmic rays, weather conditions, etc.
The ultra-high frequency (UHF) trans- mission signals in the range of 300–3000 MHz may lose their strength due to fading (a phenomenon of troposphere). Modulation (attenuation) noise: The behavior of the communication channel is affected by the modulation techniques we choose for the transmission of the signal. This noise is also referred to as attenuation noise and has been defined in two main classes: amplitude- frequency and phase-frequency attenuation distortions.
In the first class of this noise (amplitude-frequency), the level of transmitted signal depends on the frequency of the signal, transmission media, distance it travels, length of communication circuits, etc. The signal varies with the frequency over the bandwidth of the signal.
This loss of level (decaying amplitude) of the transmitted signal is not the same for all frequencies, and this non-uniform variation of the transmitted signal across the bandwidth causes amplitude-frequency distortion. Installing inductive padding coils in the channel circuit at regular intervals can reduce this type of noise, which introduces lumped inductance over the channel.
This scheme defines a uniform decay of the ampli- tude of the signal over the channel. Another method of reducing the noise is line condi- tioning, which is being used with leased voice-grade communication. In the case of switched networks, equalizers are attached with modems and they nullify the effects of the noise on the channel. The second type of attenuation distortion (phase frequency) is caused by the fact that signals do not vary linearly with both frequency and phase shift and, as such, consist of a large number of frequency components. These frequency components have different.
Phase shifts with respect to frequency, travel at different speeds, and arrive at the receiving side at different instants of times in different order. This type of noise is also known as delay distortion or envelope delay, phase distortion, or simply delays.
Loaded cables, hybrid circuits, or filters (if used in the communication circuits) can cause the noise. Interestingly, these sources of noise also cause phase jitter. This noise is not serious for voice-grade communication but becomes a major problem with data communication. It can be reduced by using the same techniques as that of the previous noise (amplitude- frequency distortion), e.g., line conditioning for leased lines or attaching equalizers with modems. Non-linear distortions: The above-described modulation (attenuation) distortions in gen- eral have deterministic behavior and affect the workings of communication circuits.
In other words, these distortions can be analyzed and measured, and protective circuits may be designed to handle these noises. There are certain distortions which are nonlinear in nature and hence offer nonlinear behavior to the communication circuits.
These distortions are usually caused by saturation effects in magnetic cores, nonlinear characteristics and behavior of the communication circuit itself, etc., and the effects become more significant if frequency-division multiplexing (FDM) is used in the systems. The difference in the carrier frequency of both transmission and receiving sides causes the harmonic relation- ship (frequency offset) and becomes a serious problem in data communications which use the narrow-frequency modulation scheme. In applications where the carrier signal at the receiving side is controlled or managed by the carrier signal generators of the transmitting side, the frequency offset may have little effect and can be controlled. Another nonlinear distortion category is inter-modulation distortion, which is caused by a frequency-division multiplexing (FDM) system where a large number of voice-grade channels are multiplexed and transmitted over high-capacity channels (coaxial cable, satellite link, etc.). The signals on two different communication circuits may interfere with each other and produce a signal possessing a frequency band (via inter-modulation) which may have been assigned to signals going through another communication circuit. Although the interference between two circuits may produce a small frequency band value compared to the ones that are transmitted, sometimes it may become intolerable. Some of you may have heard unwanted conversation or dial tones in your receiver.
This noise may become serious in data communication if the modem is transmitting a high-amplitude signal at a constant frequency. This noise can be reduced if signals are of a low amplitude level and of variable frequency.
Quantization noise: This type of noise occurs with a pulse-coded modulation (PCM) signal. In the PCM process, an analog signal is encoded in terms of quantization levels, which are obtained by sampling the signal (using Nyquist’s Law). The number of bits which are included and transmitted usually determine the values of the samples.
On the receiving side, during demodulation, this distortion may be a serious problem. Increasing the number of bits in the samples can reduce the noise, thus reducing the number of steps required for the quantization process to transmit the signal. This in turn reduces the number of steps required at the receiving side, too. Obviously, we can not increase the number of bits in the samples to just any value; it is constrained by the available bandwidth of the PCM channel. Digita l distortion: This type of distortion occurs in the DTE/DCE interface if the standard defined by the EIA is not properly and strictly followed. The noise is caused by the difference in the sample transition, different signal values at different transitions, different times to restore the decaying amplitude of the digital signal, etc. As a result of this, the transition from one logic to another takes different times and causes errors in data information.
An appropriate logic error occurs at the receiving side if it takes more time than at the other side to reproduce it. These different timings of logic values may be caused due to a non-uniform sampling rate generated by a sampling clock.
It is interesting to note that the same sources may also cause timing jitter noise. T iming jitter: The synchronizing pulses generated by clocks sometimes are not stable and are affected by various factors such as instability in the electronic circuits (due to feedback), unwanted signals, etc. The signals generating high-frequency components obviously expe- rience more distortion (attenuation) than the low-frequency components and, as a result, these components are going to be out of sync on the time scale.
This type of distortion is called timing jitter. Electronic circuits have many stages of operations. The output generated by one stage supplies clock pulses to the next stage electronic circuit, which in turn supplies pulses to the following, and so on. If signals are generated during each clock pulse, which will also be regenerated at the repeaters, this provides both signals: the actual data signal and the signal generated by the noise. A small number of signals generated during the clock pulses may have little effect on the synchronization, but in the case of excessive signals, both sides will be out of sync, causing the non-functioning of the clock. Letting the data link protocol recover so-called “lost packets” (during the excessive timing jitter) by bypassing the lost frame can reduce the noise. This way, the synchronization between transmitter and receiver will be maintained.
Baseband bias distortion: Signals from computers and terminals are square wave pulses. These pulses experience some losses due to the parameters of communication links. These parameters include resistance, inductive and capacitive effects, and shunt resistance. These parameters oppose the flow of signals and, as such, are distorted. The resistance offered by the link opposes the flow of signals, and the resistance offered by it is dependent on the frequency and distance.
The baseband signals are generally used for low frequencies over a longer distance. The inductance opposes the rate of change of current flow through the link and, as a result, the changes in the logic (1 to 0 or vice versa) are distorted and the rise or fall of the pulses gets distorted. The opposition to the rate of change of flow of pulses corresponds to a resistance given by reactance of inductance.
The capacitive effect opposes the rate of change of voltage levels of logic and, as a result, the original varying signal gets opposed by varying voltage in opposite direction. This distorts the pulses. The reactance of capacitance usually depends on parameters such as frequency, wire diameter, type of insulation, etc. The shunt resistance represents the losses due to current flowing into insulators or dielectric or hysteresis losses and is dependent on frequency, external environmental conditions, etc. These causes provide significant inter- ference between the signal pulses, which are distorted, and this situation is known as bias distortion.
This distortion does not include the effects of propagation delay of the link. Changing the sampling rate and its threshold value can change this type of distortion. A higher sampling threshold may reduce this distortion.
Rename.html –.php menggunakan perintah mv Cukup dengan menggunakan perintah mv.html.php 3.2. Perintah-perintah shell selain bash. Bourne Shell (sh) sh adalah shell standar Unix yang dibuat tahun 1979 oleh Stephen Bourne dari AT&T dengan memakai bahasa pemrograman Algol. Sh terkenal karena sederhana, compact, and cepat. Kelemahannya adalah kurang interkatif seperti tidak ada history, aliasing, dan job control.
Default prompt shell sh adalah $ (dolar). C Shell (csh) csh memiliki feature yang lebih lengkap dibandingkan sh. Shel ini dibuat tahun 1970an oleh Bill Joy dari University of California at Berkeley dengan menggunakan bahasa C.
Fitur yang terdapat dalam csh antara lain command-line history, aliasing, built-in arithmetic, filename completion, dan job control. Kelemahnnya adalah karena didesain untuk mesin skala besar dan memiliki banyak fitur maka shel ini cenderung lambat bila digunakan pada mesin kecil. Default prompt shell csh adalah% (persen). Korn Shell (ksh) Korn shell merupakan pengembangan dari bourne shell yang ditulis oleh David Korn dari AT&T pada pertengahan 1980an. Feature Korn shell antara lain editable history, aliases, functions, regular expression wildcards, built-in arithmetic, job control, coprocessing, dan special debugging.
Default prompt shell ksh adalah $ (dolar). Bourne Again Shell (bash) Bash merupakan default shell Linux yang merupakan pengembangan dari bourne shell sehingga kompatibel juga di Unix. Shell ini dibuat pada tahun 1988 oleh Brian Fox dari FSF GNU.
Fitur yang dimiliki bash antara lain interaktif, dapat membuat shortcut, bisa berwarna, dll. Default Bash prompt adalah $ (dolar).