31,114 research outputs found
Coherent Perfect Rotation
Two classes of conservative, linear, optical rotary effects (optical activity
and Faraday rotation) are distinguished by their behavior under time reversal.
In analogy with coherent perfect absorption, where counterpropagating light
fields are controllably converted into other degrees of freedom, we show that
only time-odd (Faraday) rotation is capable of coherent perfect rotation in a
linear and conservative medium, by which we mean the complete transfer of
counterpropagating coherent light fields into their orthogonal polarization.
This highlights the necessity of time reversal odd processes (not just
absorption) and coherence in perfect mode conversion and may inform device
design.Comment: 4 pages, 2 figure
q-series and L-functions related to half-derivatives of the Andrews--Gordon identity
Studied is a generalization of Zagier's q-series identity. We introduce a
generating function of L-functions at non-positive integers, which is regarded
as a half-differential of the Andrews--Gordon q-series. When q is a root of
unity, the generating function coincides with the quantum invariant for the
torus knot.Comment: 21 pages, related papers can be found from
http://gogh.phys.s.u-tokyo.ac.jp/~hikami
The influence of an oil recycler on emissions with oil age for a refuse truck using in service testing
A method of cleaning lubricating oil on line was
investigated using a fine bypass particulate filter followed
by an infra red heater. Two bypass filter sizes of 6 and 1
micron were investigated, both filter sizes were effective
but the one micron filter had the greatest benefit. This
was tested on two nominally identical EURO 1 emissions
compliance refuse trucks, fitted with Perkins Phazer
210Ti 6 litre turbocharged intercooled engines and coded
as RT320 and RT321. These vehicles had emissions
characteristics that were significantly different, in spite of
their similar age and total mileage. RT321 showed an
apparent heavier black smoke than RT320. Comparison
was made with the emissions on the same vehicles and
engines with and without the on-line bypass oil recycler.
Engine exhaust emissions were measured about every
400 miles. Both vehicles started the test with an oil drain
and fresh lubricating oil. The two refuse trucks were
tested in a different sequence, the RT320 without the
recycler fitted and then fitted later and the RT321 with
the recycler fitted and then removed later in the test and
both without any oil change. The RT320 was also the
one with the finer bypass filter. The test mileage was
nearly 8,000 miles both trucks. The air/fuel ratio was
worked out by the exhaust gas analysis. The correlation
between air/fuel ratio and emission parameters was
determined and appropriate corrections were made in
the case of that the air/fuel ratio had an effect on
emissions. The results showed that the on line oil
recycler cleaning system can reduce the rate of increase
of the NOx with oil age. There appeared little influence of
the oil recycler on carbon monoxide and hydrocarbon
emissions. The rate of increase in particulate emissions
was reduced by 50% for RT320 and an immediate
decrease in particulate emissions was seen on RT320
test after fitting the recycler. The black smoke was
reduced by 30% for RT320 in terms average value and
an immediate decrease in smoke after fitting the recycler
on RT320 test and an immediate increase in smoke after
the removal of the recycler on RT321 test were shown
Effects of an on line bypass oil recycler on emissions with oil age for a bus using in service testing
A method of cleaning lubricating oil on line was
investigated using a fine bypass particulate filter
followed by an infra red heater. Two bypass filter
sizes of 6 and 1 micron were investigated, both filter
sizes were effective but the one micron filter had the
greatest benefit. This was tested on two nominally
identical EURO 2 emissions compliance single
decker buses, fitted with Cummins 6 cylinder 8.3 litre
turbocharged intercooled engines and coded as Bus
4063 and 4070. These vehicles had emissions
characteristics that were significantly different, in
spite of their similar age and total mileage. Bus 4063
showed an apparent deterioration on emissions with
time while Bus 4070 showed a stabilised trend on
emissions with time for their baseline tests without
the recycler fitted. Comparison was made with the
emissions on the same vehicles and engines with
and without the on-line bypass oil recycler. Engine
exhaust emissions were measured about every 2000
miles. All tests started with an oil drain and fresh
lubricating oil. The two buses were tested in a
different sequence, Bus 4063 with the recycler fitted
and then removed later in the test after an oil change
and Bus 4070 with no recycler fitted at first and then
fitted after 29,000 miles with no oil change. The Bus
4070 was also the one with the finer bypass filter.
The test mileage was 45,000 miles for Bus 4063 and
48,000 miles for Bus 4070. The air/fuel ratio was
worked out by the exhaust gas analysis. The
correlation between air/fuel ratio and emission
parameters was determined. The results showed that
the on line oil recycler cleaning system reduced the
rate of increase of the NOx from 5% to 1.6% for Bus
4063 and from 4.1% to 0% for Bus 4070 per 10,000
miles. Hydrocarbon emissions increased 30 ppm per
10,000 miles with the recycler removed compared to
a stabilised level with the recycler fitted for Bus 4063.
There was a small decrease in hydrocarbon
emissions after fitting the recycler for Bus 4070. The
particulate emissions were reduced by 35% for Bus
4063 and 24% for Bus 4070 on average. The
reductions on total particulate mass were due to
reductions on particulate carbon and lube oil VOF
emissions. The black smoke was reduced by 56% for
Bus 4063 in terms of rate of increase and 40% for
Bus 4070 in terms of average value
Education In Forestry
This article is written with the intention of clearing up some questions that the high school student in Iowa who is considering a Forestry course may have in mind. Possibly it will help answer some such questions as these
Optimal Invariant Similar Tests for Instrumental Variables Regression
This paper considers tests of the parameter on endogenous variables in an instrumental variables regression model. The focus is on determining tests that have some optimal power properties. We start by considering a model with normally distributed errors and known error covariance matrix. We consider tests that are similar and satisfy a natural rotational invariance condition. We determine tests that maximize weighted average power (WAP) for arbitrary weight functions among invariant similar tests. Such tests include point optimal (PO) invariant similar tests. The results yield the power envelope for invariant similar tests. This allows one to assess and compare the power properties of existing tests, such as the Anderson-Rubin, Lagrange multiplier (LM), and conditional likelihood ratio (CLR) tests, and new optimal WAP and PO invariant similar tests. We find that the CLR test is quite close to being uniformly most powerful invariant among a class of two-sided tests. A new unconditional test, P*, also is found to have this property. For one-sided alternatives, no test achieves the invariant power envelope, but a new test -- the one-sided CLR test -- is found to be fairly close. The finite sample results of the paper are extended to the case of unknown error covariance matrix and possibly non-normal errors via weak instrument asymptotics. Strong instrument asymptotic results also are provided because we seek tests that perform well under both weak and strong instruments.Instrumental variables regression, invariant tests, optimal tests, similar tests, weak instruments, weighted average power
Asymmetric Ejecta of Cool Supergiants and Hypergiants in the Massive Cluster Westerlund 1
We report new 5.5 GHz radio observations of the massive star cluster Westerlund 1, taken by the Australia Telescope Compact Array, detecting nine of the ten yellow hypergiants (YHGs) and red supergiants (RSGs) within the cluster. Eight of nine sources are spatially resolved. The nebulae associated with the YHGs Wd1-4a, -12a and -265 demonstrate a cometary morphology - the first time this phenomenon has been observed for such stars. This structure is also echoed in the ejecta of the RSGs Wd1-20 and -26; in each case the cometary tails are directed away from the cluster core. The nebular emission around the RSG Wd1-237 is less collimated than these systems but once again appears more prominent in the hemisphere facing the cluster. Considered as a whole, the nebular morphologies provide compelling evidence for sculpting via a physical agent associated with Westerlund 1, such as a cluster wind
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