3,987 research outputs found
Techniques and errors in measuring cross- correlation and cross-spectral density functions
Techniques and errors in measuring cross spectral density and cross correlation functions of stationary dynamic pressure dat
An Adaptive Partial Response Data Channel for Hard Disk Magnetic Recording
An adaptive data channel is proposed which is better able to deal with the variations in
performance typically found in the recording components of a hard disk drive. Three such
categories of variation were investigated in order to gain an understanding of their relative
and absolute significance; variations over radius, along the track length, and between
different head / media pairs. The variations were characterised in terms of their effects on
the step-response pulse width and signal-to-noise ratio. It was found that in each of the
categories investigated, significant variations could be found in both longitudinal and
perpendicular recording systems which, with the exception of radial variations, were nondeterministic
over different head / media pairs but were deterministic for any particular head
/ media pair characterised.
Conventional data channel design assumes such variations are non-deterministic and is
therefore designed to provide the minimum error rate performance for the worst case
expected recording performance within the range of accepted manufacturing tolerance. The
proposed adaptive channel works on the principle that once a particular set of recording
components are assembled into the disk drive, such variations become deterministic if they
are able to be characterised. Such ability is facilitated by the recent introduction of partial
response signalling to hard disk magnetic recording which brings with it the discrete-time
sampler and the ability of the microprocessor to analyse signals digitally much more easily
than analogue domain alternatives.
Simple methods of measuring the step-response pulse width and signal to noise ratio with
the partial response channel's electronic components are presented. The expected error rate
as a function of recording density and signal to noise ratio is derived experimentally for the
PR4 and EPR4 classes of partial response. On the basis of this information and the
recording performance it has measured, the adaptive channel is able to implement either
PR4 or EPR4 signalling and at any data rate. The capacity advantage over the non-adaptive
approach is investigated for the variables previously identified. It is concluded on the basis
of this investigation that the proposed adaptive channel could provide significant
manufacturing yield and capacity advantages over the non-adaptive approach for a modest
increase in electronic complexity
Design study of tradeoffs in spacecraft tape recorder development Final engineering report
Tradeoff design study in spacecraft tape recorder developmen
Effects of boom-corridor thinning on harvester productivity and residual stand structure
Biomass derived from small-diameter, dense, thinning stands is largely underutilized within the European Union, mainly because of in-effective harvesting methods and cutting technology, leading to high supply costs. Therefore, the efficacy of boom-corridor thinning (BCT) and selective thinning (ST) on harvester felling and bunching productivity was compared for the first thinning of whole tree biomass in small-diameter, dense stands. BCT working method is when trees are cut with linear movements of the harvester's boom reach, along narrow corridors, instead of cutting each tree selectively (ST). Trials were performed in six forest stands, one in Sweden, two in Finland, and three in Slovenia, using the same harvester and operator. A time-and-motion study was carried out in 64 pre-marked study units (32 replications per method), across a variety of stand conditions. The biomass removal for both treatments averaged 40.2 dry t ha -1 and BCT productivity averaged 5.4 dry t PMh -1. For BCT, harvester work time consumption (sec tree -1) and productivity (dry t PMh -1) were on average 27% lower and 16% higher, respectively, compared with ST. The effectiveness of the accumulating felling head technology used could potentially be increased by implementing a feed-roller system when handling excessive tree lengths. Developing dedicated harvesting technology for BCT could further boost productivity, facilitating cost-effective and sustainable utilization of low-value small-diameter tree biomass and replacing fossil resources
A bibliography /with abstracts/ on gas-lubricated bearings Interim report
Gas lubricated bearings - annotated bibliograph
Enhanced coding, clock recovery and detection for a magnetic credit card
Merged with duplicate record 10026.1/2299 on 03.04.2017 by CS (TIS)This thesis describes the background, investigation and construction of a system
for storing data on the magnetic stripe of a standard three-inch plastic credit
in: inch card. Investigation shows that the information storage limit within a 3.375 in
by 0.11 in rectangle of the stripe is bounded to about 20 kBytes. Practical issues
limit the data storage to around 300 Bytes with a low raw error rate: a four-fold
density increase over the standard. Removal of the timing jitter (that is prob-'
ably caused by the magnetic medium particle size) would increase the limit to
1500 Bytes with no other system changes. This is enough capacity for either a
small digital passport photograph or a digitized signature: making it possible
to remove printed versions from the surface of the card.
To achieve even these modest gains has required the development of a new
variable rate code that is more resilient to timing errors than other codes in its
efficiency class. The tabulation of the effects of timing errors required the construction
of a new code metric and self-recovering decoders. In addition, a new
method of timing recovery, based on the signal 'snatches' has been invented to
increase the rapidity with which a Bayesian decoder can track the changing velocity
of a hand-swiped card. The timing recovery and Bayesian detector have
been integrated into one computation (software) unit that is self-contained and
can decode a general class of (d, k) constrained codes. Additionally, the unit has
a signal truncation mechanism to alleviate some of the effects of non-linear distortion
that are present when a magnetic card is read with a magneto-resistive
magnetic sensor that has been driven beyond its bias magnetization.
While the storage density is low and the total storage capacity is meagre in
comparison with contemporary storage devices, the high density card may still
have a niche role to play in society. Nevertheless, in the face of the Smart card its
long term outlook is uncertain. However, several areas of coding and detection
under short-duration extreme conditions have brought new decoding methods
to light. The scope of these methods is not limited just to the credit card
Atomisers for the Aerial Application of Pesticides in Tsetse (Glossina sp) and Armyworm (Spodoptera exempta) Control
Aerial application of insecticides is likely to remain an important component in
realistically-costed vector and migratory pest control operations for the foreseeable
future. The objective of this work was to identify or design improved atomisers for
use in two such operations, tsetse (Glossina sp. ) and African armyworm
(Spodoptera exempta) control, the former requiring an insecticide aerosol ýx'ith a
VMD of 20 to 30ýim at rates upto 0.5 litres/minute and the latter a fine spray with a
VMD of 80 to 120ýtm at rates around 16 litres/minute. In both cases rotary
atomisation was confirmed as the most appropriate technique.
Assessments were made of seven commerciall%, available atomisers and two existinc,
prototypes, on the basis of existing reports and new data generated under simulated
flight conditions in a wind tunnel. Droplet sizing was carried out using an optical
array probe set to give a resolution of 54m over a range of 3.6 -3) 12.54m. None of
the atomisers tested met the specification for tsetse-spraying, the limiting factors
being rotation speed and inability to distribute low volumes of liquid across their full
atomising surface. The Micronair AU4000 and AU5000 and the Micron X-I were
found to be suitable for armyworm control, the Micron X-1 having the additional
ability to produce spray with VMDs down to 40ýim.
A review of rotary atomiser literature provided design guidelines for the design of an
atomiser capable of meeting tsetse specifications. The principle effect of liquid flow
4D
within the atomiser was found to be on the uniformity of fluid distribution.
Premature ligament formation and formation of cross-flow vortices were identified
as factors which could adversely influence fluid distribution under some conditions.
Ligzan ment seperation from disks can be aided byI slender teeth, providing that these
have a spaciniz similar to the natural spacing of ligaments predicted by Taylor
instability theoInry . The effect of rotation speed and atomiser diameter on droIp let
diameter is determined by the degree of stretching of the ligament due to its
acceleration relative to the atomiser, implying that a finer spray would be achieved
using a smaller rotating diameter disc than a larger diameter disc with the same
peripheral speed.
A series of experimental studies was carried out usinrgD higZDh speed photogZ_r_a phy in
conjunction with the droplet sizinaprobe. Disturbancesh a,,i,n, g the forrn predicted for
C
cross-flow vortices were observed in liquid on a plain spinning disc. A sin(-)'Ieligament
generator was constructed. With increasing rotation speed this rt\'taled a
series of increasingly unstable ligament disintegration modes in which interaction
with the surroundin4g15 air became a controlling-- factor. Complete shattering of the
ligament occured at a Weber number of between 4 and 5, similar to reported values
for liquid jets in a cross flo%v of cyas. Droplet sizing indicated that the specified
performance for tsetse operations could be obtained from 50mm diameter atomisers
with a total of around _'30000is suing points at a rotation speed of 26000 RPNI. This
Zý
sucy(yestecdN l,i ndcr rather than disc-based atomisers.
A slit was found to be impractical as a means of distributing liquid unifom-ily at high
rotation speeds but distribution was sucýe: ssfully achieved using a porous flow
resistor. Prototype wind- and electi-ically-driven atornisers were constructed using
rotating porous cylinders fed internally by spray bars designed with the help of finite
element methods. Ligament formation was found to occur from a film of liquid on
the outer surface of the cylinder, the variation in spacing with feedrate and rotation
speed suggesting Taylor instability to be the controlling factor. The prototype
atomisers achieved a performance suitable for tsetse control operations. This was not
enhanced by the provision of discrete issuing points
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