Re: Obama likes science ...
- From: bill.sloman@xxxxxxxx
- Date: Thu, 30 Apr 2009 14:18:34 -0700 (PDT)
On Apr 30, 9:51 pm, John Larkin
<jjlar...@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
On Thu, 30 Apr 2009 10:12:08 -0700 (PDT), bill.slo...@xxxxxxxx wrote:
On Apr 30, 5:34 pm, John Larkin
<jjlar...@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
On Thu, 30 Apr 2009 07:37:42 -0700 (PDT), bill.slo...@xxxxxxxx wrote:
On Apr 30, 3:19 am, John Larkin
<jjlar...@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
On Tue, 28 Apr 2009 21:08:16 -0700 (PDT), bill.slo...@xxxxxxxx wrote:
On Apr 29, 2:16 am, krw <k...@xxxxxxxxxxxxxxxxx> wrote:
On Tue, 28 Apr 2009 17:03:39 -0700, Jim Thompson
<To-Email-Use-The-Envelope-I...@xxxxxxxxxxxxxxx> wrote:
On Tue, 28 Apr 2009 15:29:14 -0700, John Larkin
<jjlar...@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
On Tue, 28 Apr 2009 23:04:59 +0200, "Bill Sloman"
<bill.slo...@xxxxxxxx> wrote:
"John Larkin" <jjlar...@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> schreef in
berichtnews:rspev4d0ubh0nt1015p3rqfspcpfgr7rcp@xxxxxxxxxx
On Tue, 28 Apr 2009 13:50:44 +0200, "Bill Sloman"
<bill.slo...@xxxxxxxx> wrote:
Obama is apparently only the fourth president to address the American
National Academy of Science. The audience apparently liked what they
heard.
http://www.boston.com/news/politics/politicalintelligence/2009/04/swi...
Makes another nice change from the previous administration.
http://online.wsj.com/article/SB124081528924558633.html#mod=article-o...
"The U.S. government is far better prepared for an outbreak than it
was when SARS awakened politicians and the public to the notion that
infectious diseases continue to be deadly, even with modern vaccines.
Prodded by SARS and the avian flu scare that followed, President
George W. Bush in 2005 issued a pandemic flu preparedness plan. Since
2006, $6.2 billion has been appropriated to stockpile antivirals, step
up surveillance and improve vaccine-making and technology."
But the report goes on to say
"But state and local health departments -- which are often the first to
detect new
infectious threats -- haven't received federal funds for pandemic flu
preparedness
since 2006. Many of the agencies have cut staff and services in the
recession."
so Dubbya's capacity to follow up was about what you'd expect from the
Katrina
debacle.
The billions of dollars worth of antivirals are there, ready to go if
needed. If he hadn't taken the threat seriously, they wouldn't be.
Gerald Ford also took the swine flu danger seriously, and the press
savaged him for it.
All O has done so far is talk, and not appoint a Cabinet member for
HHS in his first 100 days.
I think it's almost done.
I *am* impressed by your ability to deflect reason with prejudices,
and your admiration for teleprompter charisma. Sadly, that sort of
judgement doesn't help with circuit design.
John
Slowman's kind of judgment can't even manage whining for a broom ;-)
He might be qualified for that job.
I'm always pleased to note that I'm the highest standard for Slowman's
disdain, but please don't feed the jerk. Let him die that most
unpleasant of deaths... alone ;-)
You're not even close. I simply ignore the nitwit (doesn't even
qualify for a filter).
krw has almost enough sense not to expose himself to critical
comment.
He doesn't seem to have John Larkin and Jim Thompson's burning desire
to parade their intellectual inadequacies, but then again, he doesn't
have much of an intellect to parade, as opposed to John Larkin and Jim
Thompson, who can be genuinely impressive when they are talking about
subjects that they know something about.
So design some electronics and show us how smart you are.
Give me a problem ...
OK. Given a 5-volt supply, 6 if you really need it, design a fairly
simple 10 mA positive current source with at least 3 volts compliance
(ie, output can be as much as +3 from ground... circuit can waste 2)
and under 10 pA/rootHz total noise above, say, 1 KHz.
I've yet to dig into the noise performance of the various current
mirrors, so I may be being overly pessimistic, but the intellectually
simplest solution - monitoring the current across a roughly 100R
resistor hung from the positve rail translates your 10pA per root Hz
into 1nV per root Hz.
Don't ignore the Johnson noise of the resistor. 100 ohms is 1.3
nV/rtHz at room temp.
Sure. I should have thought of that faster. I did come up with it for
myself within about an hour, but I was cooking dinner at the time. The
route I followed won't win any prizes - I finally managed to remember
that the AD797 (and the LT1028) aren't worth paying for for source
resistances over about 50R, which has about the same level of Johnson
noise, which then prompted me to drag out my copy of "The Art of
Electronics" and find the formula (on page 431) which gives 1.27nV per
root Hz for a 100R resistor.
That would means that you were going to have to monitor the current
with a single supply amplifier that has the same sort of noise
performance as the AD797, which would more or less meet that
specification. The requirement for a positive current source with a 0V
to 3V output compliance range pretty much forces you to hang the
voltage sensing resistor off the positive rail, which in practice
restricts you to rail-to-rail op amps, rather than single supply
parts.
Why so?
Single supply op amps tend not to work when the inputs are biased
within a volt of the positive rail - IIRR there was one exception, but
I'd be surprised if it were still available. Rail-to-rail op amps can
be less restricted.
If you put a step-up transformer with a decent primary inductance in
series with the resistor, I'd imagine that you could kill most of the
current noise with a second AC-coupled feedback loop - you should be
able to get enough voltage gain out of the transformer to let you get
away with a low-noise FET input op amp whic would offer negligible
input current noise, but this wouldn't be a simple solution.
Nice idea, except this is going into a 15T magnetic field. And it
would need a radical transformer over this bandwidth.
You specified neither the external magnetic field nor the bandwidth
required. 15T would certainly saturate any core material that I know
of, but the magnet generating that field would be a superconductor,
which opens up other possibilities.
Tell me what you are actually trying to do - you know my e-mail
address - since I presume the stable 10ma current to be a means to an
end, rather than an end in itself.
But keep thinking.
I'm always thinking about something. At the moment its rarely a
rewarding activity.
--
Bill Sloman, Nijmegen
.
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