WELCOME TO THE 105B COMMENT PAGE, 2004 <HR>
2004/01/06<BR>
In the example for the 2D cylindrical geometry section, why does sintheta
correspond to the m = plus/minus 1 components? I am not sure where this
came from. In the real problem, the potential is piecewise and constant.
Does this mean that m=0 only? Also, what method should we use to graph the
field?<BR>SIN THETA =( EXP(I THETA) - EXP(-I THETA))/2 I , WHICH IS WHERE
THE M=+- 1 COMPONENTS COME FROM. YOY CAN USE ANY METHOD YOU WANT FOR THE
GRAPHS.<HR>

2004/01/09<BR>
I don't know if it's just me but the links to the mathematica notes do not
work. Sam <BR> SORRY, THE LINK IS NOW FIXED <HR>

2004/01/13 <BR>
For problem 8, if we can rewrite the given operator in Sturm-Liouville
form (set q(x) to zero and p(x) to 1) and use the inner product in the
book, since the Sturm-Liouville is hermitian with respect to that?<BR>
YES, REWRITE THE OPERATOR IN STURM-LIOUVILLE FORM<HR>

Wednesday 14th of January 2004 07:37:41 AM<BR>When I login to WebCT and
click on the 105 link, it only shows a page for 105A.  If I click on
DropBox it takes me to a list of the assignment dates for 105A, not B.<BR>
THE GOOD PEOPLE WHO RUN WEBCT FOR US HAVE MEESSED UP THE WEB SITE SOMEHOW.
IT WILL BE FIXED ASAP <hr>
LOOKS LIKE THE WEBCT PAGE HAS BEEN FIXED (WED,  JAN. 14, 11:35 AM). 

Thursday 15th of January 2004 10:11:33 PM<BR>Professor Dubin, I\'ve heard
that we\'re a week behind in lecture and I know you\'re trying to catch
up, but is there any way you could slow down a bit in lecture? I\'ve been
mostly lost the last two lectures because you\'ve been going so fast, and
other students have commented to me that they\'re also having trouble
keeping up.<br> OK, I'LL TRY. BUT I'M ACTUALLY NOT TRYING TO CATCH UP. 
IF WE'RE A WEEK BEHIND, THATS THE WAY IT IS.<hr>
Saturday 17th of January 2004 01:45:40 PM<BR>Dr. Dubin-
I believe that I speak for all the students when I say that it is a huge
detriment to our education that we do not have a Thursday lab session in
which to work on the problems.  The absence of this session causes not
only \"overloading\" of the TAs and yourself during the Friday sesson but
also in effect punishes those of us who do not wish to procrastinate.
Speaking for myself, I seldom had to attend the Friday session last
quarter; I found that by working on the problems in advance, I was able to
start my weekend early on easy weeks and to deal with the problems
completely on harder weeks.  I think it is critical to add in some TA time
prior to the day on which the assignments are due.  Thank you for
listening and I hope that you will take my comments into consideration.  
Sincerely,
Ben<BR> THERE ARE ONLY SO MANY HOURS AVAILABLE FOR HELP FROM THE TA (LAST
QUARTER, WE HAD TWICE AS MANY STUDENTS, AND QUALIFIED FRO TWICE THE TA
HELP). I CAN'T ASK HIM TO ADD HOURS TO HIS SCHEDULE. ALL I CAN DO IS SHIFT
TIME TO A DIFFERENT DAY. WE COULD MAKE THE TA'S OFFICE HOUR ON THURSDAY
FOR EXAMPLE. <P> NOTE HOWEVER, THAT THE  FIRST FEW TIMES I TAUGHT THIS
CLASS, I HAD THE LAB SCHEDULED ON A DAY BEFORE ASSIGNMENTS WERE DUE,
THINKING THIS WOULD ALLOW PEOPLE TO GET A HEAD START ON THE WORK. FEW
PEOPLE SHOWED UP, BECAUSE MOST LEFT THE WORK TO THE LAST MINUTE. AT THE
TIME, MOST AGREED THAT HAVING THE LAB ON THE DAY ASSIGNMENTS WERE DUE WAS
A BETTER PLAN, SO YOU MAY NOT SPEAK FOR ALL THE STUDENTS.   PERHAPS WE
SHOULD TAKE A POLL.<p>
<FONT COLOR="RED">OK, I WILL BE DOING MY OFFICE HOUR IN THE LAB ON
THURSDAY
FROM 3 TO 3:50,
AND MIKE THE TA WILL ALSO DO HIS OFFICE HOUR ON THURSDAY NOW, FROM 2-3.
HOPE THIS HELPS. </FONT><hr>

Tuesday 20th of January 2004 09:27:41 PM<BR>Dr. Dubin- On problem 1f from
this weeks hw, i am confused about two things.  First, how is one supposed
to define rho bar?  I have a u that I obtained by solving laplaces eq.
Second, once we have rho bar, are the eigenmodes always defined for
homogenous conditions (as in the example)? Or is there some other way of
defining them, and if so, how?  Any help or advice would be appreciated,
seeing as I am stuck on the second part of the problem. <BR> rhobar is
defined by Eq. (4.3.5). If you used Laplaces equation to solve for u, then
rhobar equals rho.  Then deltaphi has homogeneous boundary conditions, .
The eigenmodes always satisfy homogeneous boundary conditions<hr>

Monday 26th of January 2004 08:54:23 PM<BR>The \"written course notes\"
link to reserves.ucsd.edu no longer works (at least, not as of
1/26/04).<br> STRANGE--THE LINK WORKS FINE FOR ME. ALL THE WRITTEN NOTES
FOR THE WHOLE QUARTER ARE THERE. SOMETIMES STUDENTS HAVE TROUBLE ACCESSING
THE LIBRARY RESERVES FROM A HOME PC. <hr>
Wednesday 28th of January 2004 02:20:14 PM<BR>Regarding phase velocity and
group velocity: if I understand correctly, vg represents the movement of
an apparent wave, not a real wave.  The apparent wave is created by the
*sequential* cresting of individual waves.  A particular wave crests
(reaches a max amplitude) then declines.  A series of these crest in
sequence and the sequence of their cresting is what we call the wave
packet.  Is this the right way to think about this?<P>


NOT EXACTLY. INDIVIDUAL WAVES, OF THE FORM EXP[I K X - W T], DO NOT HAVE
SPATIALLY VARYING AMPLITUDES. THE MOVING WAVE PACKET WITH VELOCITY VG IS A
SUPERPOSITION OF MANY WAVES ALL WITH ALMOST THE SAME WAVENUMBER K0. THE
SUPERPOSITION CREATES AN AMPLITUDE THAT VARIES IN SPACE. <P>


If so, then are the individual waves actually moving as they evolve with
time or are they merely *standing* in a point in space but with a
time-variant amplitude?<P>


IN A FRAME MOVING WITH THE WAVEPACKET, ONE WILL SEE INDIVIDUAL WAVES IN
THE PACKET MOVING AT VPHI-VG. THEY SEEM TO APPEAR AT ONE END OF THE PACKET
AND TRAVEL TO THE OTHER. 
<hr>
Monday 08th of March 2004 12:13:06 PM<BR>Would it be possible to post
solutions to the homeworks 6,7 and 8?

Thanks <p>hmwk 8 can stll be handed in (with late decuction) but hmwk 6
and 7 are now posted <hr>

Tuesday 09th of March 2004 11:22:43 AM<BR>When a wave breaks into solitons
due to nonlinearity, do the solitons continue to propogate in the same
direction as the original wave? <p> In general, I don't know. For solitons
in the kdV equation, only propagation to the right is allowed.
<hr>