[RASMB] torque strength

[Walter Stafford]

Dear RASMBers

With regard to the UV absorbance at short wavelengths, I would like 
to add that we take spectra and catalogue them for all our sapphire 
windows. The absorbance at short wavelength varies quite a bit from 
window to window. With a careful choice of windows, one can work down 
to 220 nm or lower. Some windows however are not much good below 
about 250 nm. If I remember correctly, the original specification 
from Beckman through Meller Optics in Rhode Island, was that the 
sapphire windows be sufficiently transparent in the UV to be used 
with the UV scanning optics on the Model-E.

Walter

p.s. I just got off the phone with Tom at Mellor Optics and he will 
email me the specs on the both the standard windows and the UV clear 
windows. I will share these with you when I get them.


At 15:20 +0000 11/17/05, pjgb at mrc-lmb.cam.ac.uk wrote:
>Dear RASMBers,
>
>Ariel's advice is fine as long as one does not wish to use short UV 
>wavelengths, where the absorption of the sapphire windows in too 
>high.
>Possibly replacing distorted epon centrepieces is simpler and cheaper.
>
>Jo
>
>--On Thursday, November 17, 2005 4:05 pm +0100 Ariel Lustig 
><ariel.lustig at bluewin.ch> wrote:
>
>>
>>Hi Karen and colleagues,
>>I can tell you only from my own experience how  I treat this  problem.
>>First of all  I use  only sapphire windows,  since  at the end  they are
>>cheaper then many broken quartz windows. Why broken ? my cell-stuff  is
>>very  old so  Epoxy centerpieces (alum-filled and  charcoal-filled) swell
>>slowly and became a bit  convext on both  flat side , so I  even  install
>>(not too  easy) in case of the  bad once DS-window gaskets between the
>>window and  the  centerpiece.  as it is obligatory for  metallic
>>centerpieces!!
>>Sure that in case of metllic centerpiece the  torque  strength is more
>>crucial  since  lack of elasticity you break easier  the  window just
>>during  closing the cell (not  the  centerpiece as you wrote ,Karen ! )
>>so 130 torque -units should  be  enough. A probleme  may be  the
>>temperature, I torque  the cell at the (coldest) temperature  the run is
>>planed , independend if  I fill the  cell at room temp.( if the sample
>>allows it). The idea is to prevent  shrinking later of the
>>centerpiece....and leaking. A bit tolerance for higher  temp. is still
>>given  with  130 t.  The Epoxy once  "suffer" more tolerance, so 120 -140
>>is  OK.
>>With time usually one gets the feeling witout looking on the torque dial
>>especially  using Epoxy once , according  the  flexibility.
>>  I don't believe that the torque  instrument is a so precise instrument
>>and unic by all users !!!  It may happen (I believe  at most of you) that
>>the screw-ring -gasket  do not lie properly on top of the upper window-
>>holder (catched in the winding or an alien element is between)  breaks ,
>>and as response you may read  a high  torque  dial but in realty the
>>centerpiece is not pressed to the  windows.
>>Just returning to  centerpiece break  during a  run , usually happens
>>with  quartz  widows. First you  have  a leak  in one  sector (may be
>>evaporation true the filling screw), the filling hight liquid  remain
>>much  higher as in the other sector, then the midle strap breaks and also
>>mostly the quartz window. (Saphire  even at  max.speed never  break.)
>>yours...ariel
>>!
>>
>
>
>
>P.J.G. Butler,
>MRC Laboratory of Molecular Biology,
>Hills Road, Cambridge, CB2 2QH, UK.
>Tel. +44 (0)1223 402296
>_______________________________________________
>RASMB mailing list
>RASMB at rasmb.bbri.org
>http://rasmb.bbri.org/mailman/listinfo/rasmb


-- 
----------------------------------------------------------
Walter Stafford
mailto:stafford at bbri.org
direct dial:    617-658-7808
receptionist:  617-658-7700
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