Typed states for the displayed outbound observations.
Source: paper_references, paper_reference_links, observed 2026-08-10T15:09:20.875059Z
Paper Citation Record · LEDGER
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness
As of 13 August 2026, this Paper Citation Record lists 53 of 53 outbound references and 0 inbound Pith citation observations for arXiv:2608.07090.
A citation records a reference. It does not transfer a finding from one paper to another.
Coverage vector
One-hop event checks from named stored sources.
Source: scholarly_work_events, retraction_status_cache, observed 2026-08-12T06:34:41.77262+00:00
Pith citing papers itemized under the disclosed page cap.
Source: paper_references, paper_reference_links
A source-named dated measurement, never combined with another source.
Source: cited_works
Reference resolution
53 of 53 outbound references displayed
- verified exact1
- verified fuzzy33
- unresolved18
- parse uncertain0
- malformed identifier1
- metadata mismatch0
External citation measurements
No source-named external measurement is stored.
Outbound references
Observation 95d26ec0-e3ee-41e4-84cb-8b2adbfd10ef · outbound
This paper cites Their derivation assumes collinear phase matching and identical refrac- tive indices for the pump, signal, and idler fields inside the nonlinear crystal.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Their derivation assumes collinear phase matching and identical refrac- tive indices for the pump, signal, and idler fields inside the nonlinear crystal
Reference 1
- Resolution
- malformed identifier
- raw_fallback, observed 2026-08-10T15:09:21.440360Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation 6a9e5695-89dc-43ad-a166-c8cf646a39a7 · outbound
This paper cites Within the approximate formulation of Ref.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Within the approximate formulation of Ref
Reference 2
- Resolution
- verified fuzzy
- raw_fallback, observed 2026-08-10T15:09:21.427597Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation b7333923-8806-4519-a287-33d24a453a88 · outbound
This paper cites Allen, M.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Allen, M
Reference 3
- Resolution
- verified fuzzy
- raw_fallback, observed 2026-08-10T15:09:21.414847Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation 395f7180-bf74-4441-8cfe-498cd11d0a38 · outbound
This paper cites an unresolved cited work.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Unresolved cited work
Reference 4
- Resolution
- unresolved
- raw_fallback, observed 2026-08-10T15:09:21.403153Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation 65bd06d3-0356-4584-836e-7ac8af62c5a0 · outbound
This paper cites an unresolved cited work.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Unresolved cited work
Reference 5
- Resolution
- unresolved
- raw_fallback, observed 2026-08-10T15:09:21.390765Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation cae3ba1a-399b-440b-ad13-0fd2b10fc028 · outbound
This paper cites an unresolved cited work.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Unresolved cited work
Reference 6
- Resolution
- unresolved
- raw_fallback, observed 2026-08-10T15:09:21.378624Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation 233af42c-4ccf-4e2d-acc1-c59814cc3e7c · outbound
This paper cites an unresolved cited work.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Unresolved cited work
Reference 7
- Resolution
- unresolved
- raw_fallback, observed 2026-08-10T15:09:21.368329Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation 782bae0e-4b37-420b-95fe-c68a21948ec8 · outbound
This paper cites an unresolved cited work.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Unresolved cited work
Reference 8
- Resolution
- unresolved
- raw_fallback, observed 2026-08-10T15:09:21.357904Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation 6f934e8d-ab95-4c20-a6f3-504805d8b4eb · outbound
This paper cites Luo, H.-S.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Luo, H.-S
Reference 9
- Resolution
- verified fuzzy
- raw_fallback, observed 2026-08-10T15:09:21.345918Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation 379014ef-a3b4-442f-a7a4-0184bc3e40c7 · outbound
This paper cites an unresolved cited work.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Unresolved cited work
Reference 10
- Resolution
- unresolved
- raw_fallback, observed 2026-08-10T15:09:21.335083Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation 2755f5a3-c94d-44a4-a3f8-472dfa0daccf · outbound
This paper cites Ecker, F.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Ecker, F
Reference 11
- Resolution
- unresolved
- no resolver link, observed 2026-08-10T15:09:20.728816Z
Source-reported events for the cited work
Unavailable: canonical work link unavailable.
Observation 83066670-0897-4461-9e57-53edf1580a62 · outbound
This paper cites an unresolved cited work.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Unresolved cited work
Reference 12
- Resolution
- unresolved
- raw_fallback, observed 2026-08-10T15:09:21.318837Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation fe2386c5-eee8-4efe-8373-97c95b3d601a · outbound
This paper cites Law and J.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Law and J
Reference 13
- Resolution
- verified fuzzy
- raw_fallback, observed 2026-08-10T15:09:21.308128Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation 787040f4-de1d-4633-b281-542374b740a1 · outbound
This paper cites Torres, A.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Torres, A
Reference 14
- Resolution
- verified fuzzy
- raw_fallback, observed 2026-08-10T15:09:21.296816Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation 318fefd0-8b02-4d62-9084-8f793487a43c · outbound
This paper cites Di Lorenzo Pires, H.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Di Lorenzo Pires, H
Reference 15
- Resolution
- verified fuzzy
- raw_fallback, observed 2026-08-10T15:09:21.286780Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation 79d735d5-9da8-48a5-9e41-8190ee1abb91 · outbound
This paper cites Nielsen and I.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Nielsen and I
Reference 16
- Resolution
- verified fuzzy
- raw_fallback, observed 2026-08-10T15:09:21.276661Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation 16183de1-4a25-438e-850e-be93ea94bed2 · outbound
This paper cites an unresolved cited work.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Unresolved cited work
Reference 17
- Resolution
- unresolved
- raw_fallback, observed 2026-08-10T15:09:21.265338Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation 042649ed-32e5-47f9-873c-0ac476226f68 · outbound
This paper cites an unresolved cited work.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Unresolved cited work
Reference 18
- Resolution
- unresolved
- raw_fallback, observed 2026-08-10T15:09:21.255249Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation 0814a160-2259-4423-91dd-fe013bb946b2 · outbound
This paper cites an unresolved cited work.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Unresolved cited work
Reference 19
- Resolution
- unresolved
- raw_fallback, observed 2026-08-10T15:09:21.244978Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation ed98c24f-636c-46eb-a04e-bbe929d8ad39 · outbound
This paper cites an unresolved cited work.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Unresolved cited work
Reference 20
- Resolution
- unresolved
- raw_fallback, observed 2026-08-10T15:09:21.234254Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation 34356841-c408-4bfe-81da-4a50ed13be99 · outbound
This paper cites Zhang, M.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Zhang, M
Reference 21
- Resolution
- verified fuzzy
- raw_fallback, observed 2026-08-10T15:09:21.224507Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation 08b5338f-524f-495a-8ebc-fd9ffe0789ff · outbound
This paper cites an unresolved cited work.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Unresolved cited work
Reference 22
- Resolution
- unresolved
- raw_fallback, observed 2026-08-10T15:09:21.215058Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation ad89883d-b414-465f-958f-ac43b002dd8b · outbound
This paper cites Salakhutdinov, E.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Salakhutdinov, E
Reference 23
- Resolution
- verified fuzzy
- raw_fallback, observed 2026-08-10T15:09:21.205904Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation 6145e17b-2657-4a03-9150-d57b42c1b82c · outbound
This paper cites Chen, Physical Review A85, 012311 (2012).
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Chen, Physical Review A85, 012311 (2012)
Reference 24
- Resolution
- verified fuzzy
- raw_fallback, observed 2026-08-10T15:09:21.195187Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation 305bc5f2-852d-4d56-8cc2-5c99ad380573 · outbound
This paper cites Wu and L.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Wu and L
Reference 25
- Resolution
- verified fuzzy
- raw_fallback, observed 2026-08-10T15:09:21.185424Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation c84a5bd4-cfce-4957-89d6-761eb975e1af · outbound
This paper cites Su and L.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Su and L
Reference 26
- Resolution
- verified fuzzy
- raw_fallback, observed 2026-08-10T15:09:21.175743Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation f2efbab2-f2fb-4683-b9ef-9c187e841c67 · outbound
This paper cites Zhang, X.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Zhang, X
Reference 27
- Resolution
- verified fuzzy
- raw_fallback, observed 2026-08-10T15:09:21.164096Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation 544137cb-0f46-4411-ad3f-b920b44e732b · outbound
This paper cites Stimulated emission tomography for efficient characterization of spatial entanglement.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Stimulated emission tomography for efficient characterization of spatial entanglement
Reference 28
- Resolution
- verified exact
- local_arxiv, observed 2026-08-10T15:09:20.909669Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation 539e66e8-c617-43e8-a30e-4abe59ffe2f3 · outbound
This paper cites Romero, D.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Romero, D
Reference 29
- Resolution
- verified fuzzy
- raw_fallback, observed 2026-08-10T15:09:21.155746Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation 36d56a82-21da-4749-baee-0f24646fcf9a · outbound
This paper cites Krenn, R.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Krenn, R
Reference 30
- Resolution
- verified fuzzy
- raw_fallback, observed 2026-08-10T15:09:21.146079Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation 1542929d-e2ac-4b03-8635-ac4262064793 · outbound
This paper cites Roger, J.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Roger, J
Reference 31
- Resolution
- verified fuzzy
- raw_fallback, observed 2026-08-10T15:09:21.136550Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation e378d9e8-6fa5-4f4c-9033-723762581cb1 · outbound
This paper cites Krenn, M.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Krenn, M
Reference 32
- Resolution
- verified fuzzy
- raw_fallback, observed 2026-08-10T15:09:21.127571Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation cc1f8ef1-20e7-4420-a4c8-f418b5bfce42 · outbound
This paper cites Zhang, M.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Zhang, M
Reference 33
- Resolution
- verified fuzzy
- raw_fallback, observed 2026-08-10T15:09:21.116787Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation 7c954a91-dd1a-4dfe-b64c-ba3209ec7582 · outbound
This paper cites an unresolved cited work.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Unresolved cited work
Reference 34
- Resolution
- unresolved
- raw_fallback, observed 2026-08-10T15:09:21.106942Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation f25c445f-af43-4d0b-a94b-ed3121f3af43 · outbound
This paper cites Bolduc, G.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Bolduc, G
Reference 35
- Resolution
- verified fuzzy
- raw_fallback, observed 2026-08-10T15:09:21.096529Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation 92810475-06b9-4232-a65b-4cc4235be18f · outbound
This paper cites Ritboon, S.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Ritboon, S
Reference 36
- Resolution
- verified fuzzy
- raw_fallback, observed 2026-08-10T15:09:21.087259Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation ebac2e86-8eb8-4912-aad3-f5c43a82e177 · outbound
This paper cites Erhard, R.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Erhard, R
Reference 37
- Resolution
- verified fuzzy
- raw_fallback, observed 2026-08-10T15:09:21.079542Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation 0ccea05d-5b7b-4355-a8a1-4dc21e09f61f · outbound
This paper cites Luo, Q.-Y.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Luo, Q.-Y
Reference 38
- Resolution
- verified fuzzy
- raw_fallback, observed 2026-08-10T15:09:21.070978Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation 6fa7ec00-c107-4418-8026-868fa40ac1e9 · outbound
This paper cites Cao, S.-C.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Cao, S.-C
Reference 39
- Resolution
- verified fuzzy
- raw_fallback, observed 2026-08-10T15:09:21.062530Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation c15d8719-dc96-4f8e-9cdd-c8a1bdcee885 · outbound
This paper cites Kysela, M.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Kysela, M
Reference 40
- Resolution
- verified fuzzy
- raw_fallback, observed 2026-08-10T15:09:21.051128Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation 728e3810-d51a-463c-99bd-fa61af97ca00 · outbound
This paper cites Baghdasaryan, F.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Baghdasaryan, F
Reference 41
- Resolution
- verified fuzzy
- raw_fallback, observed 2026-08-10T15:09:21.038935Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation 550e1786-3164-4281-827c-5abb8ce3bde7 · outbound
This paper cites Schwaller, G.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Schwaller, G
Reference 42
- Resolution
- verified fuzzy
- raw_fallback, observed 2026-08-10T15:09:21.028518Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation df2d067a-6480-4306-bae5-ef8aac1f3803 · outbound
This paper cites Karan, R.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Karan, R
Reference 43
- Resolution
- verified fuzzy
- raw_fallback, observed 2026-08-10T15:09:21.020355Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation c641b704-8099-4161-bde8-4a1023643d00 · outbound
This paper cites Sevilla-Guti´ errez, V.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Sevilla-Guti´ errez, V
Reference 44
- Resolution
- verified fuzzy
- raw_fallback, observed 2026-08-10T15:09:21.012209Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation 593ceb28-2c5e-4b7f-980b-e59d475ca1df · outbound
This paper cites Miatto, D.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Miatto, D
Reference 45
- Resolution
- verified fuzzy
- raw_fallback, observed 2026-08-10T15:09:21.003472Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation b8d9b2a4-4fec-4f17-9b48-4d7fe3cd4982 · outbound
This paper cites an unresolved cited work.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Unresolved cited work
Reference 46
- Resolution
- unresolved
- raw_fallback, observed 2026-08-10T15:09:20.994432Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation b7529c7c-bb2f-415f-a8c5-66eb2b6d3a45 · outbound
This paper cites Kulkarni, L.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Kulkarni, L
Reference 47
- Resolution
- verified fuzzy
- raw_fallback, observed 2026-08-10T15:09:20.984390Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation d77b2560-855c-424d-9c7c-991b3a02eaf4 · outbound
This paper cites an unresolved cited work.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Unresolved cited work
Reference 48
- Resolution
- unresolved
- raw_fallback, observed 2026-08-10T15:09:20.974482Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation 16f5219f-14b4-4542-a4d3-a994c1d70071 · outbound
This paper cites Hong and L.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Hong and L
Reference 49
- Resolution
- verified fuzzy
- raw_fallback, observed 2026-08-10T15:09:20.963121Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation c6887659-fdb1-4ad5-ba82-4fabe32d332b · outbound
This paper cites an unresolved cited work.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Unresolved cited work
Reference 50
- Resolution
- unresolved
- raw_fallback, observed 2026-08-10T15:09:20.953392Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation e01ceb54-2c60-4952-9523-66baa0e0e6dd · outbound
This paper cites Karan, S.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Karan, S
Reference 51
- Resolution
- verified fuzzy
- raw_fallback, observed 2026-08-10T15:09:20.943919Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation 92046243-9e58-4c17-9ebd-6e85f36c3c4b · outbound
This paper cites an unresolved cited work.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Unresolved cited work
Reference 52
- Resolution
- unresolved
- raw_fallback, observed 2026-08-10T15:09:20.932750Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Observation 152bc039-0b8f-42fe-8bc9-cab5fb40bf46 · outbound
This paper cites Kulkarni, R.
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness Kulkarni, R
Reference 53
- Resolution
- verified fuzzy
- raw_fallback, observed 2026-08-10T15:09:20.920922Z
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-12T06:34:41.77262+00:00.
Pith citing papers
No inbound Pith citation observations are available.