X-ray crystallography - 2025 ACF Regionals

Question

Incomplete measurements from CCDs in this technique can lead to a loss of information called the “phase problem.” For 10 points each:

[10e] Name this technique that uses low-wavelength light to probe lattice structures. Rosalind Franklin used this technique to determine the structure of DNA.

ANSWER: X-ray crystallography [or X-ray diffraction or XRD]

[10m] X-ray crystallography is limited in scale by the diffraction limit for this quantity usually measured in angstroms. A coefficient of 1.22 appears in the Rayleigh criterion for this quantity.

ANSWER: resolution [accept angular resolution; accept resolving power; prompt on angle]

[10h] Molecular modelling using X-ray crystallography uses this quantity defined by summing differences in structure factors over all reflections. A “free” form of this quantity is usually one tenth the resolution.

ANSWER: R-factor [or R-value; accept R-free; accept discrepancy index]

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Summary


California	2025-02-01	Y	3	13.33	100%	33%	0%
Florida	2025-02-01	Y	2	25.00	100%	100%	50%
Lower Mid-Atlantic	2025-02-01	Y	6	10.00	83%	0%	17%
Midwest	2025-02-01	Y	6	10.00	100%	0%	0%
North	2025-02-01	Y	3	13.33	67%	33%	33%
Northeast	2025-02-01	Y	5	14.00	100%	20%	20%
Overflow	2025-02-01	Y	5	20.00	100%	40%	60%
South Central	2025-02-01	Y	2	20.00	100%	100%	0%
Southeast	2025-02-01	Y	4	12.50	100%	0%	25%
UK	2025-02-01	Y	10	13.00	100%	30%	0%
Upper Mid-Atlantic	2025-02-01	Y	8	16.25	88%	63%	13%
Upstate NY	2025-02-01	Y	3	10.00	100%	0%	0%

Data


Claremont A	Claremont B	10	0	0	10
UC Berkeley A	UC Berkeley B	10	10	0	20
UCLA	UCSD	10	0	0	10
Florida B	Valencia A	10	10	0	20
Florida A	Florida State A	10	10	10	30
Virginia Tech A	Duke	10	0	10	20
Liberty A	Wake Forest	0	0	0	0
UNC B	Liberty B	10	0	0	10
Virginia A	South Carolina	10	0	0	10
UNC C	Liberty C	10	0	0	10
Illinois A	Chicago A	10	0	0	10
Illinois B	Chicago D	10	0	0	10
Chicago C	Illinois C	10	0	0	10
Indiana A	Indiana B	10	0	0	10
WashU B	Missouri	10	0	0	10
WashU A	Missoui S&T	10	0	0	10
Carleton	Minnesota B	0	0	0	0
Iowa State	Wisconsin A	10	10	10	30
Winona State	Wisconsin B	10	0	0	10
BU	UMass Boston	10	0	0	10
Harvard A	Brandeis A	10	10	0	20
Harvard B	Brandeis B	10	0	0	10
Brown A	Dartmouth A	10	0	0	10
MIT A	Tufts A	10	0	10	20
UNC D	William & Mary	10	0	0	10
Purdue	Georgetown B	10	10	10	30
Iowa	Georgetown A	10	0	0	10
Northwestern A	Notre Dame C	10	0	10	20
Notre Dame B	Northwestern B	10	0	0	10
Stanford B	Notre Dame A	10	10	10	30
ASU	TAMU	10	10	0	20
Texas A	Texas B	10	10	0	20
Louisville A	Alabama A	10	0	0	10
Georgia Tech C	Georgia Tech A	10	0	10	20
Vanderbilt A	Tennessee A	10	0	0	10
Bruin A	Georgia Tech D	10	0	0	10
Cambridge A	Cambridge E	10	10	0	20
Cambridge B	Warwick B	10	10	0	20
Warwick A	Cambridge C	10	0	0	10
Bristol	Cambridge D	10	0	0	10
Oxford B	Durham	10	0	0	10
Imperial A	NYU C	10	0	0	10
LSE	Oxford C	10	0	0	10
Sheffield	Imperial B	10	0	0	10
Oxford A	Southampton A	10	10	0	20
Southampton B	Manchester	10	0	0	10
Columbia B	NYU A	10	10	0	20
Haverford A	Columbia C	10	10	0	20
John Jay College	Maryland A	10	0	0	10
Johns Hopkins A	Vassar A	10	10	10	30
Maryland B	Penn A	10	0	0	10
Yale A	NYU B	10	10	0	20
Rutgers A	George Washington A	10	0	0	10
Cornell D	Binghamton A	10	0	0	10
ESF A	RIT A	10	0	0	10
Cornell C	RIT B	10	0	0	10
George Washington B	Penn B	0	10	0	10