[3dem] Slowly varying magnetic fields
Henning Stahlberg
henning.stahlberg at unibas.ch
Wed Jun 3 12:33:36 PDT 2009
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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