[3dem] Re: Slowly varying magnetic field

Fri Jun 5 05:22:42 PDT 2009

Dear Amedee and John,

As we learned from Physics a magnetic field is generated by electric
current and the field always forms closed loop/path from 'N' pole to 'S'
pole, elevators, trains,  clouds and other fast moving things carrying
electric charge could generate magnetic field. You can use the magnetic
field detector to measure the strength and direction of the magnetic
field at different locations in/out of the buildings, that may tell you
if one of or both 'N' and 'S' pole is located inside your buildings. NMR
and MRI generate strong magnetic fields, but they have both 'N' and 'S'
pole close to each other and the field lines should not be able to
escape too far away from the machines. If the magnetic field is from
outside of your buildings, it would be difficult to shield off. An
artificial active 'N'/'S' pole circuit device could be build to guide
the magnetic field lines pass around the microscopes as Dr Stokes put in
the CM200 room at Skirball institute, NYU.

Good luck,

Dan Shi

Lab of Cell Biology,

National Cancer Institute, NIH

________________________________

From: Amedee des Georges [mailto:ad2720 at columbia.edu] 
Sent: Thursday, June 04, 2009 3:58 PM
To: 3dem at ncmir.ucsd.edu
Subject: [3dem] Re: Slowly varying magnetic field

Dear John,

We have similar problems on our F30 here in New York, even though our
room is shielded and has an active field compensation system. We haven't
been able to find where the problem come from yet. If anybody has had
that problem and has solved it, we are also interested in hearing about
it. 

Amedee

Amedee des Georges

Howard Hughes Medical Institute
Columbia University Medical Center
Black Building Room 2-221
630 West 168th Street
New York, NY 10032-3702
ad2720 at columbia.edu <mailto:rg2502 at columbia.edu> 
Phone: 212-305-9524
Fax: 212-305-9500

On Jun 4, 2009, at 3:00 PM, 3dem-request at ncmir.ucsd.edu wrote:

	Today's Topics:

	  1. Slowly varying magnetic fields (John Rubinstein, U of T)
	  2. Re: Slowly varying magnetic fields (Henning Stahlberg)

	From: "John Rubinstein, U of T" <john.rubinstein at utoronto.ca>

	Date: June 3, 2009 3:23:23 PM EDT

	To: 3dem at ncmir.ucsd.edu

	Subject: [3dem] Slowly varying magnetic fields

	Dear Colleagues,

	We recently identified a slow varying magnetic field (e.g.
changes on the time scale of ~1 second) in our microscope room.  Looking
at our FEI engineer's EMF meter, the minimal 60 Hz AC fields in the room
appear to be carried on a (much larger) background that resembles the
rising and falling of an ocean surface (but less regular).  This pattern
would be quite pretty to look at if the fields did not cause random
displacement of our electron beam of up to  ~5 mm on the phosphor screen
at 600 kx magnification (Tecnai F20 operating at 200 kV).  These fields
were not present 2 years ago when we installed the microscope.  We are
not near any elevators and our room is on the 3rd floor so we know we
are far from any subway tracks.  These "DC" fields are strongest as you
go up in our room, but are stronger in our room than in the room above
ours.  The only ductwork and wires in our ceiling are those we put in
for our air conditioner and dehumidifier and the fields persist with
this equipment turned off.  Naturally, I am concerned that something has
changed far away in the building causing these effects and that the
fields are being transmitted to our room via metal beams or rebar.

	Has anybody come across this sort of problem before, identified
the source of the fields, and/or solved the problem in some way?  Any
insight from experience would be greatly appreciated.

	Best regards,
	John

	-- 
	John Rubinstein
	Molecular Structure and Function Program
	The Hospital for Sick Children
	555 University Avenue, Rm. 3330
	Toronto, ON
	Canada
	M5G 1X8
	Tel: (+001) 416-813-7255
	Fax: (+001) 416-813-5022
	www.sickkids.ca/research/rubinstein

	From: Henning Stahlberg <henning.stahlberg at unibas.ch>

	Date: June 3, 2009 3:33:36 PM EDT

	To: "John Rubinstein, U of T" <john.rubinstein at utoronto.ca>,
3dem at ncmir.ucsd.edu

	Subject: Re: [3dem] Slowly varying magnetic fields

	Hi John,

	Do you have NMR or MRI machines nearby?

	Henning.

	___________________________________________________

	Henning Stahlberg
	Center for Cellular Imaging and Nanoanalytics (C-CINA)
	Structural Biology and Biophysics, Biozentrum,
	WRO-1058, Mattenstrasse 26
	University Basel, CH-4058 Basel, Switzerland
	Tel: +41 - 61 - 387 32 62 (office)
	Tel: +41 - 61 - 387 32 27 (administrative assistant)
	Fax: +41 - 61 - 387 39 86
	mailto:Henning.Stahlberg at unibas.ch
	Skype:henningstahlberg
	http://stahlberglab.org
	http://2dx.org
	___________________________________________________

	On Jun 3, 2009, at 9:23 PM, John Rubinstein, U of T wrote:

	Dear Colleagues,

		We recently identified a slow varying magnetic field
(e.g. changes on the time scale of ~1 second) in our microscope room.
Looking at our FEI engineer's EMF meter, the minimal 60 Hz AC fields in
the room appear to be carried on a (much larger) background that
resembles the rising and falling of an ocean surface (but less regular).
This pattern would be quite pretty to look at if the fields did not
cause random displacement of our electron beam of up to  ~5 mm on the
phosphor screen at 600 kx magnification (Tecnai F20 operating at 200
kV).  These fields were not present 2 years ago when we installed the
microscope.  We are not near any elevators and our room is on the 3rd
floor so we know we are far from any subway tracks.  These "DC" fields
are strongest as you go up in our room, but are stronger in our room
than in the room above ours.  The only ductwork and wires in our ceiling
are those we put in for our air conditioner and dehumidifier and the
fields persist with this equipment turned off.  Naturally, I am
concerned that something has changed far away in the building causing
these effects and that the fields are being transmitted to our room via
metal beams or rebar.

		Has anybody come across this sort of problem before,
identified the source of the fields, and/or solved the problem in some
way?  Any insight from experience would be greatly appreciated.

		Best regards,

		John

		-- 

		John Rubinstein

		Molecular Structure and Function Program

		The Hospital for Sick Children

		555 University Avenue, Rm. 3330

		Toronto, ON

		Canada

		M5G 1X8

		Tel: (+001) 416-813-7255

		Fax: (+001) 416-813-5022

		www.sickkids.ca/research/rubinstein

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