a practical english grammar free pdf

... far. In the affirmative a long way is more usual than far, and a long way away is more usual than far away: They sailed a long way He lives a long way away But very far away is possible, and ... an hour or individual letters spoken with a vowel sound: an L-plate an MP an SOS an 'x' a/an is the same for all genders: a man a woman an actor an actress a table 2 Use of a/an a/an ... of: a bit of news a grain of sand a pot of jam a cake of soap a pane of glass a sheet of paper a drop of oil a piece of advice C Many of the nouns in the above groups can be used in a particular

Ngày tải lên: 18/04/2021, 11:55

... Trang 1ỉ arses A.J Thomson A.V Martinet NGỮ PHÁP T ENG ANH Trang 3AJ THOMSON & A.V MARTINErBÀI TÂP NGỮ PHÁP TIẾNG ANH A PRACTICAL ENGLISH GRAMMAR EXERCISES HONG ĐỨC ... because smoke rising from the wood might attract attention 30 I h a d amazing experience last night I s a w dinosaur e a tin g meat pie i n , London park You mean you h a d nightmare ... about article in the paper He was in very bad temper 22 If you go by train you can have qaite comfortable journey, but make sure you get express, not train that stops at all the stations

Ngày tải lên: 22/10/2022, 09:50

... animal studies indicate that exposure through inhalation to vapors of acetaldehyde causes nasal tumors in rats and laryngeal tumors in hamsters However, no adequate data are available regarding acetaldehyde ... people are inconclusive, while animal studies have shown cancers of the brain and mammary glands.9a The U.S EPA has classified acrylonitrile as a group B1, meaning that it is a probable human carcinogen.9a–9c ... aniline is a probable human carcinogen.30 The IARC has observed that aniline may be catego-rized as group 3, meaning that it is not classifiable as a human carcinogen, although laboratory rats exposed

Ngày tải lên: 18/06/2014, 22:20

... Molecular formula—arsenic (As), arsenic acid (H3AsO4), arsenous acid (H3AsO3), arsenic trioxide (As2O3), arsine, arsenic trihydride (AsH3), cadmium arsenide (Cd3As2), gallium arsenide (GaAs), lead ... weakness and malaise, anorexia, nausea, diarrhea, nocturia, abdominal pain, diffuse nodular fibro-sis, respiratory hypersensitivity, asthma, sensation of hotness, cardiomyo-pathy, lung damage, ... prostration, and death.1,2,4,26 Cobalt and cancer: Nonradioactive cobalt has not been found to cause cancer in humans or animals However, cancer has been shown in animals that breathed cobalt or

Ngày tải lên: 18/06/2014, 22:20

... 161 variable optical attenuator (VOA), 213 Vernier effect, 231 vertical cavity surface-emitting lasers (VCSELs), 173-174 advantages, 173 drawbacks, 173 tunable, 180-181 two-dimensional array, ... Spanke architecture, 205-206 illustrated, 206 nonblocking, 205 Trang 7Spanke-Bene~ architecture, 207 spatial dilation, 305 drawbacks, 305 illustrated, 306 spatial reuse, 551,555 spatial walk-off ... 324-325 scrambling, 241 advantage of, 241 SONET standard, 274 SDH networks, 12, 278, 364 basic signal rate, 367 channel layer, 543 extra traffic support, 546 high-reliability services, 366 management

Ngày tải lên: 02/07/2014, 12:21

... specified, and the service may accept data at any bit rate and any protocol format within these limits It may also be able to carry analog data Transparency in the network provides several advantages An ... between is a practical network that handles digital signals at a range of bit rates up to a specified maximum Most optical networks being deployed today fall into this category Although we talk about ... physical layer is a complex task with a variety of parameters to be taken into consideration For this reason, it is very difficult to build and operate a network that can support analog as well as

Ngày tải lên: 02/07/2014, 12:21

... transmission has been all about how to transmit data at the highest capacity over the longest possible distance and is remarkable for its rapid progress What is equally remarkable is the fact that researchers ... commercially viable EDFAs spurred the deployment of a completely new generation of systems A major advantage of EDFAs is that they are capable of amplifying signals at many wavelengths simultaneously ... Channel standard for similar applications In the telecommunications world, standardization and mass deployment of SONET in North America and the similar SDH network in Europe and Japan began All

Ngày tải lên: 02/07/2014, 12:21

... energy from a lower-wavelength signal to a higher-wavelength signal is a fundamental effect that is also the basis of optical amplification and lasers The energy of a photon at a wavelength k ... 0"251002 I (a) 3 rad/s - 3 ~ -0"5 r a d / ~ 3 Figure 2.19 The phase (a), instantaneous frequency (b), and chirp (c) of an initially unchirped Gaussian pulse after it has propagated a distance ... examples we compute Pulses used in optical communication systems have finite temporal widths, and hence are not monochromatic They are also not plane w a v e s ~ t h a t is, they have a transverse

Ngày tải lên: 02/07/2014, 12:21

... is an attractive alternative to lithium niobate modulators because it can be fabricated using the same material and techniques used to fabricate semiconductor lasers This allows an EA modulator ... packaging cost In fact, transmitter packages that include a laser, external modulator, and wavelength stabilization circuits are becoming commercially available for use in WDM systems External ... undesirable effects, particularly chirp Several types of external modulators are commercially available and are increasingly being integrated with the laser itself inside a single package Trang

Ngày tải lên: 02/07/2014, 12:21

... multiplicative gain and denoted by Gm The multiplicative gain of an APD can be made quite large and even infinite a condition called avalanche breakdown However, a large value of Gm is also accompanied ... wavelengths for a number of semiconductor materials In l_xGaxAs is a ternary compound semiconductor material where a fraction 1 - x of the Ga atoms in GaAs are replaced by In atoms In l-xGaxAsyPl_y ... is a quaternary compound semiconductor material where, in addition, a fraction 1 - y of the As atoms are replaced by P atoms By varying x and y, the band gap energies and cutoff wavelengths can

Ngày tải lên: 02/07/2014, 12:21

... digital in nature it can be controlled in an analog fashion by controlling the voltage. Thus this technology can be used to realize a variable optical attentuator (VOA) as well. In fact the VOA ... signal into lower-speed bit streams. The basic unit of this serial approach is a crossbar fabricated as a single IC. Today, 64 x 64 crossbar ICs operating at 2.5 Gb/s line rates are commercially ... usually care about the input wavelength, as long as it is in the 1310 or 1550 nm window. The laser is usually a fixed-wavelength laser. A variable output can be obtained by using a tunable laser.

Ngày tải lên: 02/07/2014, 12:21

... proportional to the bit rate. Assuming the spectral width is approximately equal to the bit rate, a 10 Gb/s external- ly modulated signal has a spectral width of 10 GHz, which is a practical number ... want a grating that introduces a large amount of chromatic dispersion over a wide bandwidth so that it can compensate for the fiber chromatic dispersion over a large length as well as a wide range ... high, because of the alternating signs of the chromatic dispersion, this approach leads to a small value of the accumulated chromatic dis- persion so that we need not worry about penalties induced

Ngày tải lên: 02/07/2014, 12:21

... errors) Assume also that the polarizations are scrambled This is the case in practical systems In systems that use polarization-maintaining fiber, the Raman interaction is enhanced, and the equation ... To calculate the effect of SRS in a multichannel system, following [Chr84], we approximate the Raman gain shape as a triangle, where the Raman gain coefficient as a function of wavelength spacing ... case of practical interest given that the Raman gain bandwidth is 125 nm and the channels within a W D M system must usually be spaced within a 30 nm band dictated by the bandwidth of optical

Ngày tải lên: 02/07/2014, 12:21

... into ATM cells and reassembles the ATM cells into user data at the destination Four ATM adaptation layers, AAL-1, AAL-2, AAL-3/4 and AAL-5, are described in ITU recommendation 1.363 (AAL-3 and AAL-4 ... video, IP packets) into ATM cells This is accomplished by an ATM adaptation layer (AAL) The main function of an AAL is segmentation and reassembly (SAR): an AAL segments the user data at the source ... and AAL-4 started life separately but have since been merged into a single AAL.) We briefly describe AAL-1 and AAL-5 AAL- 1 AAL-1 is meant for transport of constant bit rate data such as circuits,

Ngày tải lên: 02/07/2014, 12:21

... switching is initiated if a signal fail or a signal degrade condition is detected on the line A signal fail represents a hard failure and is detected typically as a loss of signal or as a loss of the ... can be associated with a specific layer in the network As we saw in Chapter 6, the SONET layer includes a path layer and a line layer Both path layer and line layer protection schemes are used ... operate at the path layer, and the latter schemes operate at the line (multiplex section in SDH) layer In many cases, path layer schemes operate end to end, rerouting traffic along an alternate

Ngày tải lên: 02/07/2014, 12:21

... be transmitted on a wavelength that is different from the packet data It could also be transmitted on a separate subcarrier channel on the same wavelength All these methods allow the header to ... approach An alternative approach is to use an optical phase lock loop to sense the relative delay between the two pulse streams Just as more than one phenomenon can be used to build an optical ... carried at a lower bit rate than the high-speed data in the packet, allow- ing for easier header processing However, given the high payload speeds involved in order to maintain reasonable bandwidth

Ngày tải lên: 02/07/2014, 12:21

... circulators, 113 cladding, 33 electric/magnetic field vectors in, 59 materials, 50 refractive index, 60 Class I safety standard, 527, 530 Class IIIa safety standard, 527 Class IIIb safety standard, ... TPONs, 604 See also protection Faraday rotator, 114 fast signaling channel, 498 fault management, 496, 507-519 alarm management, 510-512 example, 507 optical trace, 509 service restoration, 507 support, ... 31,439 layers within optical layer, 504 management standards, 722-723 optical networking standards, 722 SDH standards, 721-722 standards, 721-723 wavelength grid, 347 wavelength standardization,

Ngày tải lên: 02/07/2014, 13:20